System and method for deterring fouling in a polymerization reactor

ABSTRACT

A catalyst composition may include a precontacted mixture of an olefin polymerization catalyst and an agent including an ammonium salt. The catalyst activity of the catalyst composition in the presence of water may be greater than if no ammonium salt were present in the catalyst composition. The ammonium salt may include a tetraalkylammonium salt, and the olefin polymerization catalyst may include a metallocene compound.

BACKGROUND

The present techniques relate to the field of organometalliccompositions, olefin polymerization catalyst compositions, and methodsfor the polymerization and copolymerization of olefins using a catalystcomposition.

This section is intended to introduce the reader to aspects of art thatmay be related to aspects of the present disclosure, which are describedand/or claimed below. This discussion is believed to be helpful inproviding the reader with background information to facilitate a betterunderstanding of the various aspects of the present disclosure.Accordingly, it should be understood that these statements are to beread in this light, and not as admissions of prior art.

As methods, processes, and equipment within chemical and petrochemicaltechnologies advance, the higher-quality, lower cost materials andproducts that result become more and more prolific in our everydaylives. In particular, simple molecular building blocks (or monomers) maybe brought together into longer chains (or polymers), through a chemicalprocess called polymerization to yield these materials. Polyolefins, atype of polymer widely consumed on an everyday basis, may be producedfrom various olefin monomers and one or more catalysts. Plastic productsfrom polyolefins are used for retail and pharmaceutical packaging (suchas display bags, bottles, and medication containers), food and beveragepackaging (such as juice and soda bottles), household and industrialcontainers (such as pails, drums and boxes), household items (such asappliances, furniture, carpeting, and toys), automobile components,fluid, gas and electrical conduction products (such as cable wrap,pipes, and conduits), and various other industrial and consumerproducts. The wide variety of residential, commercial and industrialuses for polyolefins has translated into a substantial demand for rawpolyolefin which can be extruded, injected, blown or otherwise formedinto a final consumable product or component.

Because of this large demand, polyolefin polymers are generally producedusing large-scale polymerization reactors, which can produce tons ofpolyolefin product in short periods of time. In typical polyolefinreaction processes, various components are added to the polymerizationreactor, which subjects the components to appropriate conditions tocause the polymerization of monomer to occur. The components can includeolefin feed components, diluent components, catalyst system components,and other additives. Upon introducing, for instance, monomer (e.g.,ethylene), comonomer (e.g., hexene), and a catalyst system (e.g., ametallocene catalyst) into the polymerization reactor underpolymerization conditions, the polymerization reaction process begins toproduce a polymer.

Because these polymerization processes are typically performed on a verylarge scale and, in some instances, on a continuous basis, the reactionconditions within the polymerization reactor may be carefully controlledin an effort to maintain the quality and reproducibility of the polymerproduct. Indeed, the polymerization reaction conditions and the types ofmaterials used in the polymerization reaction may determine the physicaland chemical properties of the polyolefin product, which can be ofparamount importance to the polymer product's marketability and ultimateuse. However, despite advances within polymerization technologies overthe past few decades, consistently obtaining polyolefins with specificproperties remains a difficult task, as precise control overpolymerization reaction variables is among the more difficult hurdlesassociated with polyolefin production.

For example, in some circumstances the polymerization conditions maycause a reactor to foul, such as when the polymerized product is formedon the reactor walls or when the product cannot be maintained as aslurry. Fouling may result in a loss in heat transfer, such as due to areduction in circulation or reduced efficiency at a heat exchangerinterface, which may impair or completely negate the capacity tomaintain the desired temperature within the reactor. A reactor foul mayalso result in a reduction in the circulation of the reactor contentsand/or in a variation from the desired percent solids (measured byvolume or by weight) of the reactor slurry. The weight percent solids(solids wt %) in the reactor may be defined as the ratio of polymer tothe total reactor contents. To the extent that a reactor foul may resultin deviations from the desired reaction conditions, the polymer productproduced during such a reactor foul may not meet the desiredspecifications; that is, the product may be “off-spec.” In extreme orrunaway fouling situations, control of the reaction may be lostentirely, and the reactor may become plugged with polymer, requiring oneto three weeks to clear, during which time the reactor may not beoperated.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the present disclosure may become apparent upon readingthe following detailed description and upon reference to the drawings inwhich:

FIG. 1 is a block flow diagram depicting a polyolefin manufacturingsystem for the continuous production of polyolefins in accordance withan embodiment of the present techniques;

FIG. 2 is a schematic overview of a reactor system having aprecontactor, where the precontactor is configured to generate acatalyst system before introduction into a polymerization reactor, inaccordance with an embodiment of the present techniques; and

FIG. 3 is a schematic diagram of a process for producing a catalystcomposition in one or more precontactors, and introducing the catalystcomposition into a polymerization reactor, in accordance with anembodiment of the present techniques.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present disclosure will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

The terminology used herein is for describing particular embodimentsonly and is not intended to be limiting of example embodiments. As usedherein, the singular forms “a”, “an” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “includes” and/or“including,” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

Although the terms first, second, primary, secondary, etc. may be usedherein to describe various elements, these elements should not belimited by these terms. These terms are only used to distinguish oneelement from another. For example, but not limiting to, a first elementcould be termed a second element, and, similarly, a second element couldbe termed a first element, without departing from the scope of exampleembodiments. As used herein, the term “and/or” includes any, and all,combinations of one or more of the associated listed items.

One factor that greatly affects the conditions within a polymerizationreactor is the activity of the catalyst used to facilitate thepolymerization process. Catalyst activity is typically understood torepresent how well a catalyst performs under specific conditions. In itsstrictest sense, a catalyst's activity can be measured based on how itaffects the kinetics (e.g., a reaction rate) of a particular chemicaltransformation or reaction sequence, and is therefore usually associatedwith a conversion rate measured under particular conditions. In thefield of large-scale polymerization, catalyst activity is often measuredin a more practical manner—the quantity of polymer produced for a givenquantity of catalyst under a given set of conditions and within acertain amount of time. Catalyst productivity also provides a measure ofthe ability of a catalyst to facilitate a particular polymerization. Asused herein, “catalyst productivity” is intended to denote a quantity ofpolymer produced per quantity of catalyst (e.g., kilograms of polymerper grams or milligrams of catalyst), while “catalyst activity” is thecatalyst's productivity over time.

Different catalysts may have different activities and/or productivities,and each catalyst may behave differently in the presence of differentreactants. Because of this, the types and quantities of reactants (e.g.,monomers, comonomers) and the types and quantities of catalysts aregenerally controlled so as to balance polymer production quantity,polymer quality, and polymer production rate, while also preventingconditions that could lead to a reactor foul. Therefore, in the contextof polymerization reactions (e.g., in large scale polymer production),many factors can affect the overall effect of a catalyst on thepolymerization process. These include, among other things, therespective concentrations of various polymerization components (e.g.,monomer, co-monomer) as well as other components that may notnecessarily be desirable, such as catalyst poisons or other contaminants(e.g., aldehydes, water). It should be noted that any discussions belowassociated with catalyst activity are also intended to encompass effectson catalyst productivity, though catalyst activity may provide a moreaccurate representation of the effects on various materials on a givencatalyst or catalyst system, at least because catalyst activity alsoprovides information related to a rate of production.

Indeed, catalyst poisons and certain other materials can have a numberof undesirable affects, such as a decrease in polymer production,polymer agglomeration, and, in some cases, reactor fouling. Ofparticular concern is water, which can be present within essentially anyfeedstock, for example in recycled diluent. Many times, feedstocks aretreated before being used in a polymerization reaction to remove as muchwater as possible, such as by distilling and/or contacting the feedstockwith a drying agent. Unfortunately, these treatment methods, whileeffective, can still leave traces of water that can negatively affectpolymerization reactions. Indeed, on an industrial scale, 2 parts permillion (ppm) water can represent a large quantity of water in thereactor.

In metallocene-based catalyst systems, water can cause the catalyst tobehave undesirably, which can lead to fouling. While not wishing to bebound by theory, it is believed that the water may cause the metallocenecatalyst system to solubilize (e.g., be removed from a solid support),causing the catalyst to have unpredictable activity and/or productivity.It should be noted that while the effect of this fouling can be polymeradherence to reactor walls and other devices (e.g., mixing devices),this type of fouling is different from static-based fouling.Specifically, it is believed that static-based fouling is not a resultof a change in catalyst activity and/or productivity, but is due tostatic buildup on polymer particles, which causes the polymer to adhereto the typically metallic surfaces of the reactor walls and mixingdevices. Regardless of the particular manner in which water causesfouling, it would be desirable if a catalyst system were able totolerate water while still having acceptable levels of activity andproductivity to produce desired polymer product.

The present inventors have found, rather surprisingly, that if apolymerization catalyst (e.g., a metallocene olefin polymerizationcatalyst) is contacted with an ammonium compound, and in particular atetraalkylammonium compound, before using the catalyst forpolymerization, the catalyst composition thus formed may be moretolerant to the presence of water in the polymerization reactor than ifthe catalyst were not previously contacted with the ammonium compound.The present inventors have also found that the amount and type ofammonium compound contacted with the polymerization catalyst can have amarked effect on whether the polymerization catalyst is able to toleratethe presence of water while maintaining acceptable levels of catalystactivity and/or productivity. In other words, in some embodiments, theunexpected results that the present inventors have achieved may bemanifest when certain ammonium compounds and the catalyst are contactedin certain relative concentrations. Example compounds and ranges arediscussed in detail below.

The conditions under which the ammonium compound and the polymerizationcatalyst are contacted may also impact the extent to which the catalystsystem operates according to the present technique. For example, whilepresent embodiments provide for any contact method to be used, incertain embodiments, one or more catalysts, or one or more catalystprecursors, one or more cocatalysts, one or more activators, or anycombination thereof, may be pre-contacted with one or more ammoniumcompounds (e.g., a tetraalkylammonium) in a precontactor upstream of apolymerization reactor, thereby forming a pre-contacted mixture and,eventually, a catalyst composition.

Contacting the ammonium compound with the catalyst in this manner may bedesirable to ensure that the contact occurs before the catalyst isintroduced into a polymerization reactor (a polymerization zone)operating under polymerization conditions (e.g., before having theopportunity to begin polymerization by contacting monomer under atemperature, pressure, and concentration sufficient to causepolymerization). Furthermore, precontacting the ammonium compound andthe catalyst (and/or catalyst precursor) ensures that the ammoniumcompound and the catalyst have sufficient opportunity to interact, whichwould otherwise be much more difficult to ensure if the ammoniumcompound and the catalyst were separately introduced into thepolymerization reactor (e.g., at different areas of the reactor and/orat different times). This is particularly true when considering therelatively small amount of the ammonium compound used in accordance withthe present technique compared to the volume of material circulatingwithin the reactor. Indeed, the amount of ammonium compound may be, insome embodiments, much less than an amount that would be used for a moretraditional additive, such as an antistatic agent.

Once formed, the catalyst systems of the present techniques are intendedfor any olefin polymerization method, using various types ofpolymerization reactors. As used herein, “polymerization reactor”includes any polymerization reactor capable of polymerizing olefinmonomers (e.g., ethylene, hexene) to produce homopolymers or copolymers.Indeed, while any suitable polymerization reactor may be used, includingbatch, slurry, gas-phase, solution, high pressure, tubular or autoclavereactors, or any combination thereof, the present techniques will bepresented in the context of a loop slurry polymerization reactor tofacilitate discussion. However, it should be noted that the discussionset forth below is intended to be applicable, as appropriate, to anypolymer manufacturing systems having any one or a combination ofpolymerization reactors and/or polymerization zones. Furthermore, thepresent embodiments are also intended to be applicable to procedureswhere the catalyst and ammonium compound are contacted with one anotherin a polymerization reactor, before the polymerization reactor isoperated under polymerization conditions. In this way, a polymerizationreactor, before polymerization, may at least partially simulate theenvironment within a precontactor.

With this in mind, various sections are set forth below to facilitatediscussion of the present techniques. In particular, Section I providesan overview of an embodiment of a polyolefin production process that mayutilize one or more ammonium compounds as fouling mitigation agents. Thepolyolefin production process includes examples of systems configured tofacilitate receiving feedstocks, including the ammonium compounds,systems configured to prepare the feedstocks for the polymerization, andvarious systems configured to process effluent from a reactor system toproduce a polymer product.

Section II provides an example embodiment of a reactor system that mayutilize one or more ammonium compounds as fouling mitigation agents. Thereactor system may include features that may be used to control the flowof various feeds into the reactor system and into a precontactor. Thefeatures may include a control system configured to produce a catalystcomposition in accordance with the present technique. Section II alsoprovides examples of monomers, comonomers, and various otherpolymerization components (additives) that may be used in thepolymerization process.

Section III provides example embodiments of catalyst compositions andcomponents in accordance with embodiments of the present techniques. Thecatalyst compositions and components include example fouling reductionagents, example metallocene compounds, example solid activator-supports,example organoaluminum compounds as cocatalysts, exampleorganoaluminoxane compounds as cocatalysts, example organoboroncompounds as cocatalysts, example ionizing compounds as cocatalysts, andnon-limiting examples of catalyst compositions.

Section IV provides example embodiments of processes that may be used toproduce a catalyst composition having a precontacted mixture of acatalyst and a fouling reduction agent. The processes may includeprecontacting a fouling reduction agent, a catalyst, a cocatalyst, asolid activator-support, and other optional components beforeintroducing the catalyst composition into a polymerization reactor, orbefore carrying out polymerization using the catalyst composition.Example relative amounts for the fouling reduction agent, catalyst,cocatalyst, and solid activator-support are also provided.

Section V provides example properties of the catalyst compositionproduced in accordance with the present techniques when used inpolymerization reactions. Example methods of determining relativefouling mitigation ability, catalyst activity and/or productivity, andwater tolerance are also provided.

In addition to the various sections noted above, comparative examples ofembodiments of the present technique are also provided. The examplesinclude a control, where fouling was intentionally initiated by theinjection of water. The examples also include reactions where differentfouling mitigation agents, including polymeric mixtures andtetraalkylammonium salts, were used to mitigate fouling due to water. Incertain of the examples, fouling was either substantially or totallymitigated, while catalyst activity was substantially unaffected.

I. Polyolefin Production Process—An Overview

In the production of polyolefins, polymerization reactors, whichpolymerize monomers into polyolefins, and extruders, which convert thepolyolefins into polyolefin pellets, are typically components ofpolymerization systems undergoing continuous operation. However, avariety of both continuous and batch systems may be employed throughoutthe polyolefin production process. Turning now to the drawings, andreferring initially to FIG. 1, a block diagram depicts an exemplarymanufacturing process 10 for producing polyolefins, such as polyethylenehomopolymer, copolymer, and/or terpolymer, or any other polymer. Varioussuppliers 12 may provide reactor feedstocks 14 to the manufacturingsystem 10 via pipelines, trucks, cylinders, drums, and so forth. Thesuppliers 12 may include off-site and/or on-site facilities, includingolefin plants, refineries, catalyst plants, on or off-site laboratories,and the like. Examples of possible feedstocks 14 include olefin monomersand comonomers (such as ethylene, propylene, butene, hexene, octene, anddecene), diluents (such as propane, isobutane, n-hexane, and n-heptane),chain transfer agents (such as hydrogen), catalysts (such as Zieglercatalysts, Ziegler-Natta catalysts, chromium catalysts, and metallocenecatalysts), co-catalysts (such as aluminum alkyl, alkyl boron, and alkylaluminoxane), solid activator-supports (e.g., solid oxides, solid oxidestreated with electron-withdrawing groups) and other additives such asantiblock agents, antistatic agents, colorants, and the like. In thecase of ethylene monomer, as an example, ethylene feedstock may besupplied via pipeline at approximately 800-1450 pounds per square inchgauge (psig) at 45-65° F. As another example, hydrogen feedstock may besupplied via pipeline at approximately 900-1000 psig at 90-110° F. Ofcourse, a variety of supply conditions may exist for ethylene, hydrogen,and other feedstocks 14.

In accordance with present embodiments, the feedstocks 14 may include afouling reduction agent 16. As discussed in further detail below, thefouling reduction agent 16 may include an ammonium salt, such as atetraalkylammonium salt, an ionic liquid, a polymer or polymeric mixturehaving the ammonium salt, a mixture having an amine-containing polymerand an acid, or any combination thereof. As depicted, the foulingreduction agent 16 may be provided to a precontactor 18, where thefouling reduction agent 16 is able to interact with certain othercomponents 20 of the polymerization reaction. These other components 20may generally include, but are not necessarily limited to, one or morepolymerization catalysts, catalyst precursors, and/or cocatalysts.Example components include metallocene catalysts, solid super acid (SSA)activator-supports, organoaluminoxane compounds, organoaluminumcompounds, Ziegler-Natta catalysts, one or more diluents, or anycombination thereof. In addition, in certain embodiments, the othercomponents 20 provided to the precontactor 18 will generally excludemonomeric components, such as olefin monomers (e.g., α-olefin monomerssuch as ethylene and 1-hexene). However, in other embodiments, 1-hexenemay be a part of the precontacted mixture in order to enhance catalystproductivity and/or activity.

In certain embodiments, the precontactor 18 is used to form aprecontacted mixture 22, which may include a catalyst system prepared inaccordance with the present techniques. Indeed, the precontactor 18 mayreceive or otherwise control (e.g., meter) the relative amounts ofcontact components (e.g., catalyst, fouling reduction agent 16, diluent)in order to precisely control the relative amount of each component toachieve the reduction in fouling described herein. In embodiments wherethe amounts of each of these components is controlled by another system(e.g., a control system and/or a feed system), the control system mayprecisely control the relative amounts of these components in order toachieve the same. Such embodiments are discussed in further detail belowwith respect to FIG. 2. Further, it should be noted that theprecontactor 18 illustrated in FIG. 1 is merely intended to be anexample, and in an actual implementation, may represent one or moreprecontactors that each generate a respective precontacted mixture. Insuch embodiments, the fouling reduction agent 16 may be provided to anyone or a combination of these precontactors.

In this regard, in embodiments where more than one pre-contactor is used(e.g., in situations where a catalyst precursor is contacted with aseries of compounds in a series of precontactors), the fouling reductionagent 16 may be mixed at any stage and in any of the precontactors, aslong as the contact occurs prior to polymerization. In this way, thefouling reduction agent 16 may be contacted with a first precontactedmixture produced from a catalyst or catalyst precursor, a secondprecontacted mixture produced from the catalyst or the catalystprecursor, a third precontacted mixture produced from the catalyst orthe catalyst precursor, and so on. The fouling reduction agent 16 mayalso be contacted with the catalyst in any one or a combination ofprecontactors, such that the fouling reduction agent 16 may have one ormore than one opportunity to interact with the catalyst.

The precontactor 18 (or precontactors) may individually be separatefrom, communicatively coupled to (e.g., fluidly coupled to), and/or maybe a part of, a reactor feed system 24 configured to provide one or morefeed streams 26 to one or more polymerization reactors of a reactorsystem 28. The feed system 24 may receive one or more of the feedstocks14 from the suppliers 12, where the feedstocks 14 may be stored. Thefeedstocks 14 may be stored in any suitable vessel, such as in monomerstorage and feed tanks, diluent vessels, catalyst tanks, co-catalystcylinders and tanks, and so forth. In certain embodiments, certainfeedstocks 14 may be treated or processed within the feed system 24before being provided to the precontactor 18. For instance, a diluentmay be distilled or otherwise subjected to some form of purification,catalysts (or portions of the catalyst) may be calcined, activated byactivator components, or otherwise pretreated.

Further, feedstocks 14 such as monomer, comonomer, and diluent, may besent through treatment beds (e.g., molecular sieve beds, aluminumpacking, etc.) to remove catalyst poisons in the feed system 24. Suchcatalyst poisons may include, for example, water, oxygen, carbonmonoxide, carbon dioxide, and organic compounds containing sulfur,oxygen, or halogens. The olefin monomer and comonomers may be liquid,gaseous, or a supercritical fluid, depending on the type of reactor orreactors within the reactor system 28. Furthermore, in operation, thefeed system 24 may also store, treat, and meter recovered reactoreffluent for recycle to the reactor system 28. Indeed, operations in thefeed system 28 generally receive both the feedstock 14 and recoveredreactor effluent streams. In certain embodiments, the recovered effluentstreams may be a potential source of water contamination.

In total, the feedstocks 14 and recovered reactor effluent are processedin the feed system 24 and fed as the feed streams 26 (e.g., streams ofmonomer, comonomer, diluent, catalysts, co-catalysts, hydrogen,additives, or combinations thereof) to the reactor system 28. Further,the feed system 24 typically provides for metering and controlling theaddition rate of the feedstocks 14 into the reactor system 28 tomaintain the desired reactor stability and/or to achieve the desiredpolyolefin properties or production rate.

The reactor system 28 may include one type of reactor in a system ormultiple reactors of the same or different type. Production of polymersin multiple reactors may include several stages in at least two separatepolymerization reactors interconnected by a transfer device making itpossible to transfer the polymers resulting from the firstpolymerization reactor into the second reactor. The desiredpolymerization conditions in one of the reactors may be different fromthe operating conditions of the other reactors. Alternatively,polymerization in multiple reactors may include the manual transfer ofpolymer from one reactor to subsequent reactors for continuedpolymerization. Multiple reactor systems may include any combinationincluding, but not limited to, multiple loop reactors, multiple gasreactors, a combination of loop and gas reactors, multiple high pressurereactors or a combination of high pressure with loop and/or gasreactors. The multiple reactors may be operated in series or inparallel.

In certain embodiments, the reactor system 28 may include a loop slurryreactor, an example of which is discussed below with respect to FIG. 2.Such reactors may include vertical or horizontal loops. Monomer,diluent, catalyst and, in some embodiments, comonomer may becontinuously fed to the loop reactor where polymerization occurs.Generally, continuous processes may include the continuous introductionof a monomer, the catalyst system formed in accordance with presentembodiments (e.g., precontacted mixture 22), and a diluent into apolymerization reactor and the continuous removal from this reactor of asuspension including polymer particles (commonly referred to as fluff orgranules) and the diluent. Reactor effluent 30, as discussed below, maybe flashed to remove the solid polymer from the liquids that include thediluent, monomer and/or comonomer. Loop slurry polymerization processes(also known as the particle form process) are disclosed, for example, inU.S. Pat. Nos. 3,248,179, 4,501,885, 5,455,314, 5,565,175, 5,575,979,6,239,235, 6,262,191 and 6,833,415, each of which is incorporated byreference in its entirety herein for all purposes.

Additionally or alternatively, the reactor system 28 may include a gasphase reactor. Such systems may employ a continuous recycle streamcontaining one or more monomers continuously cycled through a fluidizedbed in the presence of the catalyst (e.g., the catalyst having beencontacted with the fouling reduction agent 16) under polymerizationconditions. A recycle stream may be withdrawn from the fluidized bed andrecycled back into the reactor. Simultaneously, polymer product may bewithdrawn from the reactor and new or fresh monomer may be added toreplace the polymerized monomer. Such gas phase reactors may include aprocess for multi-step gas-phase polymerization of olefins, in whicholefins are polymerized in the gaseous phase in at least two independentgas-phase polymerization zones while feeding a catalyst-containingpolymer formed in a first polymerization zone to a second polymerizationzone. Example gas phase reactors are disclosed in U.S. Pat. Nos.5,352,749, 4,588,790 and 5,436,304, each of which is incorporated byreference in its entirety herein for all purposes.

According to still another aspect of the techniques, the reactor system28 may, in addition to or in lieu of other types of reactors, include ahigh pressure polymerization reactor. By way of example, the highpressure reactor may include a tubular reactor or an autoclave reactor.Tubular reactors may have several zones where fresh monomer, initiators,or catalysts are added. Monomer may be entrained in an inert gaseousstream and introduced at one zone of the reactor. Initiators, catalysts,and/or catalyst components (e.g., a contacted mixture of the foulingreduction agent 16 and the catalyst) may be entrained in a gaseousstream and introduced at another zone of the reactor. The gas streamsmay be intermixed for polymerization. Heat and pressure may be employedappropriately to obtain appropriate polymerization reaction conditions.

According to yet another aspect of the techniques, the reactor system 28may, in addition to or in lieu of other types of reactors, include asolution polymerization reactor wherein the monomer may be contactedwith the catalyst composition (e.g., a contacted mixture of the foulingreduction agent 16 and the catalyst) by suitable stirring or otheragitation features. A carrier including an inert organic diluent orexcess monomer may be employed. If desired, the monomer may be broughtin the vapor phase into contact with the catalytic reaction product, inthe presence or absence of liquid material. The polymerization zone maybe maintained at temperatures and pressures that will result in theformation of a solution of the polymer in a reaction medium. Agitationmay be employed to obtain better temperature control and to maintainuniform polymerization mixtures throughout the polymerization zone. Theexothermic heat of polymerization may be dissipated using adequatecooling media, such as a coolant within a cooling jacket, air from aheat rejection system, or the like.

The particular type of reactor or reactors used within the reactorsystem 28 may determine, at least in part, the throughput of the reactorsystem 28 and the properties of the polymer product that may beobtained. For example, the reactor effluent 30, as noted above, mayinclude polymer particulates (e.g., fluff or granules) having one ormore melt, physical, rheological, and/or mechanical properties ofinterest, such as density, melt index (MI), melt flow rate (MFR),copolymer or comonomer content, modulus, and crystallinity. Operatingparameters of the one or more reactors of the reactor system 28, such astemperature, pressure, flow rate, mechanical agitation, product takeoff,component concentrations, polymer production rate, and so forth, may beselected to achieve the desired polymer properties.

After leaving the reactor system 28, the reactor effluent 30 may besubsequently processed, such as by an effluent treatment system 32, toseparate non-polymer components 34 (e.g., diluent, unreacted monomer,and catalyst) from polymer fluff 36. The recovered non-polymercomponents 34 may be processed, such as by a fractionation system 38, toremove heavy and light components. Fractionated product streams 40 maythen be returned to the reactor system 28 via the feed system 24. Inaddition, some or all of the non-polymer components 34 may recycle moredirectly to the feed system 24 via a non-fractionated product stream 42,bypassing the fractionation system 38. Additionally, in someembodiments, the fractionation system 38 may perform fractionation ofthe feedstocks 14 before introduction into the feed system 24. Forexample, monomer components may be separated from diluent components,such that any one or combination of polymerization components may becontrollably fed into the reactor system 28.

The polymer fluff 36 may be further processed within the effluenttreatment system 32 and/or in an extrusion/loadout system 44, asdescribed below. Although not illustrated, polymer granules and/oractive residual catalyst intermediate in the effluent treatment system32 may be returned to the reactor system 28 for further polymerization,such as in a different type of reactor or under different reactionconditions.

In the extrusion/loadout system 44, the polymer fluff 36 is typicallyextruded to produce polymer pellets 46 with the desired mechanical,physical, and melt characteristics. Extruder feed may contain additives,such as UV inhibitors and peroxides, which are added to the polymerfluff 36 to impart desired characteristics to the extruded polymerpellets 46. An extruder/pelletizer within the extrusion/loadout system44 receives the extruder feed, containing the polymer fluff 36 andwhatever additives have been added. The extruder/pelletizer heats andmelts the extruder feed which then may be extruded (e.g., via a twinscrew extruder) through a pelletizer die of the extrusion/loadout system44 under pressure to form the polyolefin pellets 46. Such pellets 46 maybe cooled in a water system disposed at or near the discharge of theextruder/pelletizer.

In general, the polyolefin pellets may then be transported to a productload-out area where the pellets may be stored, blended with otherpellets, and/or loaded into railcars, trucks, bags, and so forth, fordistribution to customers 48. In the case of polyethylene, the pellets46 shipped to the customers 48 may include low density polyethylene(LDPE), linear low density polyethylene (LLDPE), medium densitypolyethylene (MDPE), high density polyethylene (HDPE), and enhancedpolyethylene. The various types and grades of polyethylene pellets 46may be marketed, for example, under the brand names Marlex® polyethyleneor MarFlex™ polyethylene of Chevron-Phillips Chemical Company, LP, ofThe Woodlands, Tex., USA.

The produced polyolefin (e.g., polyethylene) pellets 46 may be used toproduce a variety of articles of manufacture, including both householdconsumer products and industrial products. By way of non-limitingexample, such articles may include adhesives (e.g., hot-melt adhesiveapplications), electrical wire and cable, agricultural films, shrinkfilm, stretch film, food packaging films, flexible food packaging, milkcontainers, frozen-food packaging, trash and can liners, grocery bags,heavy-duty sacks, plastic bottles, safety equipment, coatings, toys andan array of containers and plastic products. To form end-products orcomponents from the pellets 46, the pellets 46 are generally subjectedto further processing, such as blow molding, injection molding,rotational molding, blown film, cast film, extrusion (e.g., sheetextrusion, pipe and corrugated extrusion, coating/lamination extrusion,etc.), and so on.

II. Mitigating Fouling in a Polymerization Reactor

As noted above, the present technique may be applicable to anypolymerization reaction (e.g., olefin polymerization reaction) performedin any appropriate polymerization reactor having one or morepolymerization zones. Indeed, the catalyst systems formed in accordancewith the present approach may be utilized in a variety of reactors inorder to mitigate fouling of the reactor, and in particular fouling dueto the presence of water, which can cause solid polymer, formed frompolymerization, to adhere to various reactor features (e.g., impellers,mixing devices, reactor walls). One example of the reactor system 28that may benefit from the present technique is depicted in FIG. 2. Inparticular, FIG. 2 depicts an embodiment of the reactor system 28 havinga loop slurry reactor 60 fluidly coupled to the precontactor 18, thefeed system 24, and the effluent treatment system 32. The loop slurryreactor 60, as depicted, includes segments of pipe (e.g., horizontalsegments 62 and vertical segments 64) connected by smooth bends orelbows 66. In these segments, polymerization components and othermaterials received from the precontactor 18 and the feed system 24 arecirculated and subjected to polymerization conditions (e.g., appropriatetemperature and pressure for polymerization).

Heat exchange devices 68 (e.g., cooling jackets) may be positioned in aheat exchange relationship with one or more of the segments, which maybe desirable to maintain the polymerization reaction within a desiredtemperature range. For example, the polymerization reaction may beexothermic, or heat-generating, which can increase the rate ofpolymerization. Accordingly, in such embodiments, the heat exchangedevices 68 may reduce the temperature of the components circulatingwithin the loop slurry reactor 60 in order to assist in maintaining adesired polymerization rate. As an example, during operation, a coolingfluid may be circulated within the cooling jackets as needed to removethe generated heat and to maintain the temperature within the desiredrange, such as between approximately 150° F. to 250° F. (65° C. to 121°C.) for polyethylene. Either or both of the reactor temperature andcoolant duty may be monitored to determine the presence of a foul, orwhether a particular fouling mitigation agent 16 is operating asdesired.

As the components circulate within the loop slurry reactor 60, forexample via the action of a motive device (e.g., a pump having animpeller positioned in the interior of the loop slurry reactor 60), thepolymerization reaction progresses and forms polymer. As noted above, incertain fouling situations, the polymer may adhere to the inner walls ofthe reactor 60. For example, solid polymer may adhere to interior wallsof the horizontal segments 62, the vertical segments 64, the elbows 66,portions of a motive device (e.g., blades of an impeller) or anycombination thereof. In these situations, circulation of the materialsmay be difficult, and can result in downtime of the reactor. In certainembodiments, fouling in this manner may be at least partiallyattributable to the presence of water in the polymerization reaction.Indeed, it should be noted that water may be present in certain recycledcomponents, such as diluent recycled from the effluent treatment system32, and even in certain feedstocks 14 obtained directly from a supplier.A load of the motive device may also be monitored to determine thepresence of a foul, or whether a particular fouling mitigation agent 16is operating as desired.

In accordance with present embodiments and as noted above, certaincomponents provided from the precontactor 18 and/or the feed system 24may assist in mitigating this and other types of fouling. Theprecontactor 18 and the feed system 24 may introduce various componentsby way of one or more reactor inlets 70. The one or more inlets 70 mayinclude reactor tap-ins, injection ports, or other types of featuresconfigured to introduce components into a polymerization zone of thereactor 60. The one or more inlets 70 may be positioned on any one or acombination of the horizontal segments 62, the vertical segments 64,and/or the elbows 66. In certain embodiments, respective positions ofthe one or more inlets 70 may facilitate introduction of the componentsinto the loop slurry reactor 60. For instance, one or more of the inlets70 may be positioned upstream of a motive device (e.g., a pump,impeller, paddle stirrer), and/or on one or more of the verticalsegments 64 to enable the components to be drawn into a reaction zone ofthe loop slurry reactor 60.

As shown by example in the illustrated embodiment, the one or moreinlets 70 may include a precontactor inlet 72 configured to enable thereactor 60 to receive the precontacted mixture 22 from the precontactor18, and first and second feed system inlets 74, 76 configured to enablethe reactor 60 to receive various feedstocks 14 from the feed system 24.In accordance with present embodiments, the precontactor 18 may producethe precontacted mixture 22 by precontacting the fouling reduction agent16 with a catalyst 78 and/or a cocatalyst 80 while other components ofthe feed system 24 (e.g., storage vessels, treatment vessels) may store,treat, and/or provide monomer, comonomer, diluent, and/or variousadditives of the feedstock 14 to the loop slurry reactor 60. In certainembodiments, components of the feed system 24 may provide the foulingreduction agent 16, the catalyst 78, the cocatalyst 80, and othercomponents to the precontactor 18.

For instance, other components of the feedstock 14 that may be providedto the precontactor 18 may include a diluent 82, which may be desirableto enable the fouling reduction agent 16 to appropriately interact withthe catalyst 78 and/or the cocatalyst 80. The diluent 82 may serve as asolvent for the fouling reduction agent 16, the catalyst 78, thecocatalyst 80, or any combination thereof, or may serve to suspend anyone or a combination of these components within the precontactor 18.Indeed, the diluent 82 may be fed into the precontactor 18 and the loopslurry reactor 60, though the diluent 82 in the precontactor 18 and theloop slurry reactor 60 may be the same or different, and may include anyone or a combination of suitable diluents.

The diluent 82 may be, for example, an inert hydrocarbon that is aliquid or a supercritical fluid at reaction conditions, depending on thedesired properties of the polymer fluff or the slurry. The diluent 82may include isobutane, propane, n-pentane, i-pentane, neopentane,n-hexane, cyclohexane, cyclopentane, methylcyclopentane,ethylcyclohexane, and the like, or combinations thereof. In the reactor60, the purpose of the diluent 82 is generally to suspend the catalystparticles and polymer. The diluent 82 may also serve as a reactionmedium or other homogenizing medium for the formation of theprecontacted mixture 22 within the precontactor 18. In certainembodiments, one or more diluents may be utilized in the precontactor 18and/or the reactor 60. Further, in certain embodiments, the diluent 82may be present as a liquid, gas, or supercritical fluid, or anycombination thereof.

It should be noted that the components provided to the precontactor 18,or any one or a combination of the precontactors in embodiments wheremultiple precontactors are present, are not limited to the foulingreduction agent 16, the catalyst 78, and the cocatalyst 80. For example,the fouling reduction agent 16, the catalyst 78, and/or the cocatalyst80 may be first contacted (e.g., in the diluent 82) to form a firstprecontacted mixture, followed by contact with a monomer 84, comonomer86, or other feed components 88 (e.g., additives) to form at least onesubsequent precontacted mixture (e.g., a second, third, or fourthprecontacted mixture).

Examples of the monomer 84 and comonomer 86 include various unsaturatedreactants. Such reactants may include olefin compounds having from about2 to about 30 carbon atoms per molecule and having an olefinic doublebond. The present techniques encompass homopolymerization processesusing a single olefin such as ethylene or propylene, as well ascopolymerization reactions with two or more different olefiniccompounds. For example, in a copolymerization reaction with ethylene,copolymers may include a major amount of ethylene (>50 mole percent) anda minor amount of comonomer <50 mole percent. The comonomers 86 that maybe copolymerized with ethylene may have from three to about 20 carbonatoms in their molecular chain.

Olefins that may be used as the monomer 84 or comonomer 86 may includeacyclic, cyclic, polycyclic, terminal (α), internal, linear, branched,substituted, unsubstituted, functionalized, and non-functionalizedolefins. For example, compounds that may be polymerized with thecatalysts of the present techniques include propylene, 1-butene,2-butene, 3-methyl-1-butene, isobutylene, 1-pentene, 2-pentene,3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 2-hexene, 3-hexene,3-ethyl-1-hexene, 1-heptene, 2-heptene, 3-heptene, the four normaloctenes, the four normal nonenes, the five normal decenes, or anycombination thereof. Further, cyclic and bicyclic olefins, including,for example, cyclopentene, cyclohexene, norbornylene, norbornadiene, andthe like, may also be polymerized as described above. In one embodiment,the monomer 84 for the catalyst compositions of the present techniquesmay be ethylene and the comonomer 86 may be 1-hexene, so that thepolymerizations may be copolymerizations of ethylene and 1-hexene. Inaddition, the catalyst compositions of the present techniques may beused in polymerization of diolefin compounds, including for example,such compounds as 1,3-butadiene, isoprene, 1,4-pentadiene, and1,5-hexadiene.

The amount of comonomer introduced into a reactor zone to produce acopolymer may be from about 0.001 to about 99 weight percent comonomerbased on the total weight of the monomer and comonomer, generally fromabout 0.01 to about 50 weight percent. In other embodiments, the amountof comonomer introduced into a reactor zone may be from about 0.01 toabout 10 weight percent comonomer or from about 0.1 to about 5 weightpercent comonomer. Alternatively, an amount sufficient to give the abovedescribed concentrations, by weight, of the copolymer produced, may beused.

In certain embodiments, it may be desirable to precontact a mixtureformed by contacting the fouling reduction agent 16 and the catalyst 78and/or cocatalyst 80 (e.g., a first precontacted mixture) with themonomer 84 and/or comonomer 86 (e.g., to form a second precontactedmixture) to enhance the activity and/or productivity of the catalystcomposition. The precontacting of the first precontacted mixture withthe monomer 84 and/or comonomer 86 may occur in the same precontactorused to contact the fouling reduction agent 16 and the catalyst 78and/or cocatalyst 80, or may occur in an additional precontactordisposed downstream from the precontactor used to contact the foulingreduction agent 16 and the catalyst 78 and/or cocatalyst 80. In thisway, the formation of multiple precontacted mixtures using one or moreprecontactors is presently contemplated. The precontacting of variouscomponents is discussed in further detail below with respect to SectionV.

The other components 88 provided to the reactor 60 may includeplasticizers (e.g. mineral oil), flow promoters, lubricants,antioxidants, initiators, mold release agents, color enhancers, and/orpolymerization aids such as chain transfer agents (e.g., alkylmercaptans such as n-dodecyl mercaptan, terpenes, alkyl and arylhalides, and alkyl aromatics). Other such additives will be apparent tothose of ordinary skill in the art and are within the scope of thepresent disclosure.

The reactor system 28 may also include various features configured tocontrol the relative amounts of the components of the feedstock 14provided to the precontactor 18, the loop polymerization reactor 60, ora combination thereof. Further, these features may be used to transfervarious feedstocks 14 between storage vessels, treatment vessels,distillation apparatuses, and so forth. By way of example, theillustrated reactor system 28 includes a control system 90 configured tocontrol the relative amounts of the feedstocks 14 provided to thedifferent components of the reactor system 28. The control system 90 mayalso, in certain embodiments, control the operation of the loop slurryreactor 60 and/or receive information related to the operation of theloop slurry reactor 60. In some configurations, the control system 90may, based on monitored operating parameters of the loop slurry reactor60, determine appropriate amounts of the feedstocks 14 and adjust theamounts as appropriate.

Generally, the control system 90 may utilize and/or include one or moreprocessing components, including microprocessors (e.g., fieldprogrammable gate arrays, digital signal processors, applicationspecific instruction set processors, programmable logic devices,programmable logic controllers), tangible, non-transitory,machine-readable media (e.g., memory such as non-volatile memory, randomaccess memory (RAM), read-only memory (ROM), and so forth. Themachine-readable media may collectively store one or more sets ofinstructions (e.g., algorithms) in computer-readable code form, and maybe grouped into applications depending on the type of control performedby the control system 90. In this way, the control system 90 may beapplication-specific, or general purpose.

The control system 90 may be a closed loop control system (e.g., doesnot use feedback for control), an open loop control system (e.g., usesfeedback for control), or may include a combination of both open andclosed system components and/or algorithms. Further, in someembodiments, the control system 90 may utilize feed forward inputs. Forexample depending on information relating to the feedstocks 14 (e.g.,compositional information relating to the catalyst 78, the cocatalyst80, the fouling reduction agent 16, the diluent 82, the monomer 84, thecomonomer 86, and/or the other feed components 88), the control system90 may control the flow of any one or a combination of the feedstocks 14into the precontactor 18 and/or the loop slurry reactor 60.

Any method of controlling the flow of each of the feedstocks 14 to theprecontactor 18 and/or through the feed system 24 and/or to the loopslurry reactor 60 is presently contemplated. The illustrated embodimentdepicts an example configuration in which the feedstocks 14 aredelivered to the precontactor 18, the feed system 24, and the loopslurry reactor 60 via a plurality of flow paths 92 and a plurality offlow control devices 94. The flow paths 92 may include one or moreconduits and one or more intermediate flow paths between an origin(e.g., a delivery area from a supplier or an injection port or zone) anda destination (e.g., a storage vessel, a reaction vessel, a treatmentvessel, a precontactor, a distillation unit). The flow control devices94 may include a pump, aspirator, impeller, flow control valve, or anycombination thereof.

In the context of the present techniques, the control system 90 maycontrol the flow of the fouling reduction agent 16 to the precontactor18 along a fouling reduction agent flow path 96 using one or morefouling reduction agent flow control devices 98. The flow of the foulingreduction agent 16 along the fouling reduction agent flow path 96 may bedetermined based on, among other things, the amount of catalyst 78and/or cocatalyst 80 in the precontactor 18 and/or being provided to theprecontactor 18, the amount of catalyst 78 and/or cocatalyst 80 in thereactor 60 and/or being provided to the reactor 60, indications of apotential fouling condition in the reactor 60, desired polymer productspecifications (e.g., desired physical and/or mechanical properties),monitored conditions within the reactor 60 (e.g., monomer and/orcomonomer concentrations, temperature, pressure, polymer productionrates), or any combination thereof.

Similarly, the control system 90 may control the flow of the catalyst 78and the cocatalyst 80 to the precontactor 18 along a catalyst flow path100 and a cocatalyst flow path 102, respectively, using one or morecatalyst flow control devices 104 and one or more cocatalyst flowcontrol devices 106, respectively. The flow of the catalyst 78 and thecocatalyst 80 along their respective flow paths may be determined basedon, among other things, the amount of fouling reduction agent 16 in theprecontactor 18 and/or being provided to the precontactor 18, the amountof fouling reduction agent present within the reactor 60 and/or beingprovided to the reactor 60, the amount of catalyst 78 and/or cocatalyst80 in the precontactor 18 and/or being provided to the precontactor 18,the amount of catalyst 78 and/or cocatalyst 80 in the reactor 60 and/orbeing provided to the reactor 60, indications of a potential foulingcondition in the reactor 60, desired polymer product specifications(e.g., desired physical and/or mechanical properties), monitoredconditions within the reactor 60 (e.g., monomer and/or comonomerconcentrations, temperature, pressure, polymer production rates), or anycombination thereof. A flow of the precontacted mixture 22 also may becontrolled based on any one or a combination of any flows into thereactor 60 (i.e., into the polymerization zone of the reactor 60)discussed herein, any one or a combination of flows into theprecontactor 18, based on various monitored parameters within thereactor 60, or any combination of these and similar variables. Forinstance, the flow of the precontacted mixture 22 may be controlledalong a precontacted mixture flow path 107 using one or moreprecontacted mixture flow control devices 109.

Amounts of the diluent 82, monomer 84, comonomer 86, and other feedcomponents 88 may be similarly (e.g., individually or together in anycombination) controlled along their respective flow paths 108, 110, 112,114 using one or more respective flow control devices 116, 118, 120,122. As illustrated, the diluent 82 may be provided to the precontactor18 along its respective flow path 108 using its respective one or moreflow control devices 116, and may also be provided to other parts of thefeed system 24 (or distributed throughout the feed system 24) using aseparate flow path 124 and one or more associated flow control devices126. Again, the monomer 84, the comonomer 86, and the other feedcomponents 88 may all be provided to the feed system 24 and, in certainembodiments, may be provided to the precontactor 18 as noted above.

Further, while illustrated as separate from the feed system 24, itshould be noted that the flow paths and flow control devices may each bea part of the feed system 24, may control their respective componentflows through the feed system 24, and may, in some embodiments, controlthe flow of the feedstocks 14 into the loop slurry reactor 60. The feedsystem 24 also may, in some embodiments, combine certain of thefeedstocks 14 and may provide these combined feedstocks to the reactor60 at the first and second feed system inlets 74, 76 via first andsecond feed system flow paths 128, 130 and using respective one or moreflow control devices 132, 134 positioned along the flow paths 128, 130.

Again, the flows of the various feedstocks 14 throughout the reactorsystem 28 may depend on a number of factors. In addition to beingcontrolled based on the various dynamic processes occurring in thereactor 60, the amounts of the fouling reduction agent 16 and thecatalyst 78 and/or cocatalyst 80 may be controlled so as to achieveinteraction between these components in specific relativeconcentrations. In accordance with certain embodiments, the foulingreduction agent 16 and the catalyst 78 and/or cocatalyst 80 may becontacted with one another in specific relative amounts so as tomitigate fouling in accordance with the present technique. In stillfurther embodiments, the fouling reduction agent 16 may be precontactedwith the catalyst 78 and/or cocatalyst 80 in an amount such that thefouling reduction agent 16 is present within the precontacted mixture 22in a certain concentration.

By way of example, the mol ratio of the catalyst 78 to the foulingreduction agent 16 may be between 0.01 mol catalyst 78 to 1.0 molfouling reduction agent 16 and 1.0 mol catalyst 78 to 0.01 mol foulingreduction agent 16, depending on the particular type of foulingreduction agent 16 employed. For instance, the amount of foulingreduction agent 16 suitable to prevent fouling in the polymerizationreaction may be less for certain compounds relative to others, such thatthe ratio of catalyst 78 to fouling reduction agent 16 may be higher forcertain fouling reduction agents 16. Indeed, it is believed that certainof the fouling reduction agents 16 discussed below, such astetraalkylammonium salts, may display foul-mitigating ability in amountsas low as 1 ppm (based on the weight of the diluent 82) or less.Presented below are examples of the fouling reduction agent 16, thecatalyst 78, the cocatalyst 80, and other components that may be used toproduce the precontacted mixture 22 (e.g., a catalyst composition)provided to the reactor 60.

III. The Catalyst Composition

As noted above, the precontacted mixture 22 may be referred to as acatalyst composition, at least in part because the precontacted mixture22 is formed by contacting the catalyst 78 (e.g., a metallocenecatalyst) with the fouling reduction agent 16 and, in certainembodiments, other components such as co-catalysts, activators, and soforth. In other words, in some embodiments, a catalyst system (e.g., acatalyst with some or all of its associated activating agents) may becontacted with the fouling reduction agent 16 to produce the catalystcompositions of the present techniques. Discussed hereinbelow arenon-limiting examples of what may constitute the different componentsused to form the catalyst composition.

A. The Fouling Reduction Agent

The fouling reduction agent 16 may be, in a general sense, an ammoniumcompound. The ammonium compound may be a single type of molecule, amixture of different types of molecules, or mixtures of components that,when mixed together, may produce transient ammonium compounds. However,as discussed in further detail below, certain ammonium compounds mayexhibit surprisingly better effects on the catalyst system compared toother ammonium compounds. Indeed, certain ammonium compounds may exhibitlittle to no foul-mitigating ability, or may mitigate fouls while alsodiminishing catalyst activity by an unacceptable amount. The ammoniumcompound used as the fouling reduction agent 16 may be defined by thegeneral formula:(R¹)(R²)(R³)(R⁴)N(X¹).In this formula, X¹ may be any suitable anion capable of forming anionic bond with the positively charged nitrogen, including conjugatebases of certain acids. X¹ may include, but is not limited to, a halide(fluoride, chloride, bromide, iodide), phosphates, triflates,bisulfates, sulfate, sulfites, fluoroborates, fluorosulfates,trifluoroacetate, fluorophosphates (e.g., hexafluorophosphate),fluorozirconates, fluorosilicates, fluorotitanates, permanganates,substituted or unsubstituted alkanesulfonate, substituted orunsubstituted arenesulfonate, or substituted or unsubstitutedalkylsulfate.

R¹, R², R³, and R⁴ may independently be, generally, carbon-based groups,including aliphatic or aromatic groups. In further embodiments, any oneor a combination of R¹, R², R³, and R⁴ may be joined such that thenitrogen is an atom in a cyclic structure. Aliphatic groups that may beused include, for example, an alkyl group, a cycloalkyl group, analkenyl group, a cycloalkenyl group, an alkynyl group, an alkadienylgroup, a cyclic group, and the like. This may include all substituted,unsubstituted, branched, and linear analogs or derivatives thereof,wherein each group may have from one to 20 carbon atoms. Thus, aliphaticgroups may include, for example, hydrocarbyls such as paraffins,alkenyls, and alkynyls. For example, the aliphatic groups may includesuch groups as methyl, ethyl, propyl, n-butyl, tert-butyl, sec-butyl,isobutyl, amyl, isoamyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl,dodecyl, 2-ethylhexyl, pentenyl, butenyl, and the like.

Aromatic groups that may be used include, for example, phenyl, naphthyl,anthracenyl, and the like. Substituted derivatives of these compoundsare also included, wherein each group may have from 4 to about 25carbons. Such substituted derivatives may include, for example, tolyl,xylyl, mesityl, and the like, including any heteroatom substitutedderivatives thereof. Heteroaromatic compounds are also contemplated.

Cyclic groups that may be used as substituents include, for example,cycloparaffins, cycloolefins, cycloacetylenes, arenes such as phenyl,bicyclic groups and the like, as well as substituted derivativesthereof, in each occurrence having from about 3 to about 20 carbonatoms. Thus, substituted heteroatom-substituted cyclic groups such asfuranyl may be included herein.

In some specific embodiments, X¹ may be a halide, sulfide, hydroxide, orphosphate (e.g., hexafluorophosphate or PO₃), and R¹, R², R³, and R⁴ maybe independently selected from a hydrogen, alkyl, branched alkyl,cycloalkyl, aryl, or alkenyl group, wherein the alkyl, branched alkyl,cycloalkyl, aryl, or alkenyl group has from 1 to 20 carbons. In certainof these embodiments, X¹ may be a halide, and R¹, R², R³, and R⁴ may be,independently, an alkyl group, each alkyl group having between 1 and 20carbons, such that the fouling reduction agent 16 is atetraalkylammonium halide salt. In accordance with present embodiments,the fouling reduction agent 16 may exhibit enhanced fouling mitigationability when X¹ is a halide (e.g., Cl) and R¹, R², R³, and R⁴ are eachan alkyl group having between 4 and 12 carbons. It should be noted that,in certain of these embodiments, the fouling reduction agent 16 mayexhibit enhanced fouling mitigation ability when R¹, R², R³, and R⁴ areeach an alkyl group having between 4 and 12 carbons, each alkyl groupbeing an unsubstituted alkyl chain (i.e., an n-alkyl group, such asn-butyl, n-pentyl, n-hexyl, n-octyl, n-nonyl, n-decyl, n-undecyl, orn-dodecyl, or any combination thereof). Isoalkyls and tertiary alkylsare also within the scope of the present disclosure, where any one or acombination of R¹, R², R³, and R⁴ are an alkyl group having between 4and 12 carbons and containing an isoalkyl or tertiary alkyl group.Surprisingly, as discussed in detail below with respect to the examples,the fouling reduction agent 16 exhibits enhanced fouling mitigationability when the fouling reduction agent 16 is tetra(butyl)ammoniumchloride or tetra(dodecyl)ammonium chloride. These specific foulingmitigation agents 16 may also substantially maintain, and in someembodiments, enhance catalyst activity (and/or productivity) compared tothe catalyst's baseline activity (and/or productivity), as discussed indetail below.

Other specific examples of the fouling reduction agent 16 include, butare not limited to: ionic liquids, polymeric ammonium compounds,mixtures of various components that may, together, form ammoniumcompounds, and the like. For example, when the fouling reduction agent16 is an ionic liquid, the fouling reduction agent 16 may be animidazolium compound. The fouling reduction agent 16 may also include amixture of compounds, such as a mixture of acids and amines, which may,in one embodiment, be present as a complex to produce transient ammoniumcompounds (polymeric ammonium compounds).

Another example of one fouling reduction agent 16 is STADIS 450®, aproprietary antistatic additive mixture available from Octel Starreon ofNewark, Del. It is believed that STADIS 450® antistatic additive is amixture including, among other components, dinonylnaphthylsulfonic acid,a proprietary nitrogen-containing polymer, a proprietarysulfur-containing polymer, 2-propanol, naphthalene, solvent naphtha, andtoluene. Other mixtures having nitrogen-containing polymers, acids,solvents, sulfur-containing polymers, and so forth, are also presentlycontemplated.

While mixtures such as STADIS 450® antistatic additive and otherantistatic agents and mixtures may be used as the fouling reductionagent 16, it should be noted that the amounts effective to mitigatefouling may be much less than the amount that would traditionally beused if the STADIS 450® antistatic additive were injected directly intothe polymerization reactor. In other words, the introduction of STADIS450® antistatic additive into the precontactor 18 may enable themitigation of fouling as a result of water to a greater extent than ifthe STADIS 450® antistatic additive were provided only to the reactor 60without any precontacting. For example, as discussed in the Examples,0.1 mL of 10 wt % STADIS 450® antistatic additive is sufficient tomitigate water-based fouling in a reaction performed in 2 L ofisobutane. Based on the weight of the solvent (about 5 kg), thisrepresents less than 5 ppm of STADIS 450® antistatic additive, which ismuch less than is typically used for the effective mitigation ofstatic-based fouling in a reactor.

Furthermore, it has been found that tetraalkylammonium salts such asn-Bu₄NCl and (n-C₁₂H₂₅)₄NCl may mitigate fouling while also enabling theactivity and/or productivity of the catalyst to remain substantiallyunaffected, while other compositions such as STADIS 450® antistaticadditive may diminish the activity and/or productivity of thepolymerization catalyst. In other words, the present inventors havefound that tetraalkylammonium salts such as n-Bu₄NCl and (n-C₁₂H₂₅)₄NClmay exhibit superior overall performance to other compositions such asSTADIS 450® antistatic additive when considering both fouling mitigationand catalyst activity and/or productivity. Indeed, even under the mostoptimized conditions of precontacting STADIS 450® antistatic additivewith the catalyst 78, tetraalkylammonium salts such as n-Bu₄NCl and(n-C₁₂H₂₅)₄NCl were found to exhibit better overall performance in thatwater-based fouling was mitigated and catalyst activity was alsosubstantially maintained.

It should be appreciated that a careful balance must be struck betweenfouling mitigation and catalyst activity and/or productivity in that iftoo much of the fouling reduction agent 16 is used in forming theprecontacted mixture 22, fouling may be mitigated while catalystactivity and/or productivity may suffer, while if too little foulingreduction agent 16 is used in forming the precontacted mixture 22,fouling may occur (or may not be mitigated to a sufficient extent).Certain compounds, when used as the fouling reduction agent 16, may notstrike this careful balance, regardless of the amount used to form theprecontacted mixture 22. Specific amounts of the fouling reduction agent16 useful for forming the catalyst compositions of the presenttechniques are discussed in further detail below with respect to SectionIV.

B. The Catalyst System

The fouling reduction agent 16, as noted above, may be contacted withthe catalyst 78, such as with a catalyst system produced using thecatalyst 78, to generate a catalyst composition. The catalyst 78 may beany suitable olefin polymerization catalyst, such as a particlesuspended in a fluid medium within the reactor 60. In loop slurrypolymerizations, the catalyst 78 begins polymerizing the monomer(s) toproduce the polymer, which may collect on the catalyst 78 to form aslurry (e.g., a suspension of the polymer in the diluent 82). Ingeneral, Ziegler catalysts, Ziegler-Natta catalysts, metallocenes, andother well-known polyolefin catalyst systems may be used. In accordancewith present embodiments, the fouling reduction agent 16 may beparticularly well-suited for metallocene catalyst systems, where ametallocene catalyst compound may be used in conjunction with (e.g.,contacted with), for example, activator-supports, organometal compounds,or any combination thereof, to form a metallocene catalyst system.Because metallocene catalyst systems are typically considered to be verysensitive to the addition of various components, where certaincomponents can, in some situations, totally diminish catalyst activityand/or productivity or cause a foul, it is believed that the resultsdiscussed herein constitute surprising and unexpected results in that,when used appropriately, certain of the fouling reduction agents 16display the opposite effect.

1. Metallocene Compounds

In certain embodiments, the catalyst 78 may be a metallocene catalystactivated (at least in part), for example, by a solid support. Compoundssuch as an organoaluminum, an organoaluminoxane, another ionizingcompound, or any combination thereof, may also be used for activation inaddition or in the alternative (e.g., as a cocatalyst). In certain ofthese embodiments, the metallocene may be deposited on the solidsupport, such that the catalyst 78 includes both the metallocenecompound and the solid support. The metallocene may be any metallocenesuitable to facilitate olefin polymerization, such as anansa-metallocene (also referred to as a “bridged” metallocene) or anunbridged metallocene. In some embodiments, a catalyst system may employboth an ansa-metallocene and an unbridged metallocene. Numerousprocesses to prepare metallocene compounds that may be employed in thepresent techniques have been reported. For example, U.S. Pat. Nos.4,939,217, 5,191,132, 5,210,352, 5,347,026, 5,399,636, 5,401,817,5,420,320, 5,436,305, 5,451,649, 5,496,781, 5,498,581, 5,541,272,5,554,795, 5,563,284, 5,565,592, 5,571,880, 5,594,078, 5,631,203,5,631,335, 5,654,454, 5,668,230, 5,705,578, 5,705,579, 6,187,880,6,509,427, 7,064,225, 7,799,721, and 8,013,177 describe such methods,each of which is incorporated by reference in its entirety herein forall purposes.

The term “bridged” or “ansa-metallocene” may refer to a metallocenecompound in which two η⁵-cycloalkadienyl-type ligands in the moleculeare linked (e.g., covalently) by a bridging moiety. While any number ofatoms may bridge the two η⁵-cycloalkadienyl-type ligands, certainansa-metallocenes benefit from being “tightly-bridged,” meaning that thetwo η⁵-cycloalkadienyl-type ligands are connected by a bridging groupwherein the shortest link of the bridging moiety between theη⁵-cycloalkadienyl-type ligands is a single atom. An unbridgedmetallocene is therefore intended to denote a metallocene structure inwhich the two η⁵-cycloalkadienyl-type ligands are not connected by abridging group.

In embodiments of the present techniques, the metallocenes used to formthe precontacted mixture 22 (including the catalyst composition) may beexpressed by the general formula:(X²)(X³)(X⁴)(X⁵)M¹.In this formula, M¹ may be any transition metal suitable for forming ametallocene compound, including but not limited to titanium, zirconium,or hafnium. X² may be an η⁵-cyclopentadienyl-type ligand, including butnot limited to an unsubstituted or substituted cyclopentadienyl ligand,an unsubstituted or substituted indenyl ligand, or an unsubstituted orsubstituted fluorenyl ligand. X³ also may be an η⁵-cyclopentadienyl-typeligand, including but not limited to an unsubstituted or substitutedcyclopentadienyl ligand, an unsubstituted or substituted indenyl ligand,or an unsubstituted or substituted fluorenyl ligand.

In certain of the embodiments where X² and X³ are substitutedη⁵-cyclopentadienyl-type ligands, one substituent on X² and X³ may be abridging group having the formula ER⁵R⁶. E may be a carbon atom, asilicon atom, a germanium atom, or a tin atom, and is bonded to both X²and X³. R⁵ and R⁶ may be independently an alkyl group or an aryl group,either of which may have up to 12 carbon atoms, or may be hydrogen. Infurther embodiments, R⁵ and R⁶ may be hydrocarbyl chains that form aring, such that respective chain termini of both R⁵ and R⁶ are bonded toE. The bridging groups may be selected to influence the activity and/orproductivity of the catalyst or the structure of the polymer produced.One or more substituents on X² and/or X³ may be a substituted or anunsubstituted alkyl or alkenyl group, which may any number of carbonatoms, such as between 1 and 12 carbon atoms.

Generally, substituents X⁴ and X⁵ may be independently: 1) F, Cl, Br, orI; 2) a hydrocarbyl group having up to 20 carbon atoms, H, or BH₄; 3) ahydrocarbyloxide group, a hydrocarbylamino group, or atrihydrocarbylsilyl group, any of which may have up to 20 carbon atoms;4) OBR^(A) ₂ or SO₃R^(A), wherein R^(A) may be an alkyl group or an arylgroup, either of which may have up to 12 carbon atoms.

Any additional substituent on the η⁵-cyclopentadienyl-type ligands X²and X³ and/or on a substituted alkyl group may be independently analiphatic group, an aromatic group, a cyclic group, a combination ofaliphatic and cyclic groups, an oxygen group, a sulfur group, a nitrogengroup, a phosphorus group, an arsenic group, a carbon group, a silicongroup, or a boron group, any of which may have from 1 to 20 carbonatoms. Alternatively, additional substituents may be present, includinghalides or hydrogen. The substituents on the η⁵-cyclopentadienyl-typeligands X² and X³ may be used to control the activity and/orproductivity of the catalyst and/or the stereochemistry of the polymerproduced (e.g., the tacticity of the polymer). An example of a class ofansa-metallocenes that may be used in accordance with presentembodiments is presented below.

In the above structure, M¹ may be zirconium, titanium, or hafnium and X⁵and X⁶ may be independently F, Cl, Br, or I. E may be C or Si and R⁵ andR⁶ may be independently an alkyl group, alkenyl group, or an aryl group,either of which may have up to 15 carbon atoms, or R⁵ and R⁶ may behydrogen. Again, the metallocenes used to form the precontacted mixture22 may have any metallocene structure suitable for forming homopolymers(e.g., ethylene homopolymers) and/or copolymers (e.g., ethylene-hexenecopolymers) having desirable physical and mechanical properties.

2. Solid Activator-Supports

As noted above, the metallocenes of the present disclosure may, incertain embodiments, be used in combination with a solid support, suchas a solid oxide support. In such embodiments, the catalyst 78 mayinclude both the metallocene and the solid support. However, in certainembodiments, they may be separate in that the solid oxide may notnecessarily be a solid support for the metallocene (e.g., themetallocene may or may not be adsorbed onto the solid support). In someembodiments, the solid oxide may be an acidic-activator support thatboth supports the metallocene component of the catalyst 78 and activatesthe metallocene molecule for polymerization. The present techniquesencompass catalyst compositions that include an acidicactivator-support, such as, for example, a chemically-treated solidoxide (CTSO). Additionally or alternatively, the activator-support ofthe present techniques may include clay minerals having exchangeablecations and layers capable of expanding. These activator supportsinclude ion-exchangeable materials, such as, for example, silicate andaluminosilicate compounds or minerals, either with layered ornon-layered structures, and any combination thereof. As discussed below,the CTSO or clay mineral may be used in combination with anorganoaluminum cocatalyst to activate the metallocene forpolymerization. The activator-support may include a solid oxide treatedwith an electron-withdrawing anion.

Various processes to prepare solid oxide activator-supports that may beused in the present techniques have been reported. For example, U.S.Pat. Nos. 6,107,230, 6,165,929, 6,294,494, 6,300,271, 6,316,553,6,355,594, 6,376,415, 6,391,816, 6,395,666, 6,524,987, and 6,548,441,describe such methods, each of which is incorporated by reference hereinin its entirety for all purposes.

The activator-support may include the contact product of a solid oxidecompound and an electron-withdrawing anion source. The solid oxidecompound may include an inorganic oxide, and may be optionally calcinedprior to contacting the electron-withdrawing anion source. The contactproduct may also be calcined either during or after the solid oxidecompound is contacted with the electron-withdrawing anion source. Inthis embodiment, the solid oxide compound may be calcined or uncalcined.In another embodiment, the activator-support may include the contactproduct of a calcined solid oxide compound and an electron-withdrawinganion source.

The activator-support may include a solid inorganic oxide material, amixed oxide material, or a combination of inorganic oxide materials thatmay be chemically-treated with an electron-withdrawing component, andoptionally treated with another metal ion. Thus, the solid oxide of thepresent techniques encompasses oxide materials such as alumina, “mixedoxide” compounds such as silica-alumina or silica-zirconia orsilica-titania, and combinations and mixtures thereof. The mixed metaloxide compounds such as silica-alumina, with more than one metalcombined with oxygen to form a solid oxide compound, may be made byco-gellation, impregnation or chemical deposition, and are encompassedby the present techniques.

Further, the activator-support may include an additional metal or metalion such as zinc, nickel, vanadium, silver, copper, gallium, tin,tungsten, molybdenum, or any combination thereof. Examples ofactivator-supports that further include a metal or metal ion include,for example, zinc-impregnated chlorided alumina, zinc-impregnatedfluorided alumina, zinc-impregnated chlorided silica-alumina,zinc-impregnated fluorided silica-alumina, zinc-impregnated sulfatedalumina, or any combination thereof.

The activator-support of the present techniques may include a solidoxide of relatively high porosity, which exhibits Lewis acidic orBrønsted acidic behavior. The solid oxide may be chemically-treated withan electron-withdrawing component, typically an electron-withdrawinganion, to form an activator-support. While not intending to be bound bytheory, it is believed that treatment of the inorganic oxide with anelectron-withdrawing component augments or enhances the acidity of theoxide. Thus, the activator-support exhibits Lewis or Brønsted aciditywhich may be typically greater than the Lewis or Brønsted acidity of theuntreated solid oxide. The polymerization activity of thechemically-treated solid oxide may be enhanced over the activity shownby an untreated solid oxide.

Suitable solid oxide materials or compounds that may be used in thechemically-treated solid oxide of the present techniques may include,for example, Al₂O₃, B₂O₃, BeO, Bi₂O₃, CdO, Co₃O₄, Cr₂O₃, CuO, Fe₂O₃,Ga₂O₃, La₂O₃, Mn₂O₃, MoO₃, NiO, P₂O₅, Sb₂O₅, SiO₂, SnO₂, SrO, ThO₂,TiO₂, V₂O₅, WO₃, Y₂O₃, ZnO, ZrO₂, and the like, including mixed oxidesthereof, and combinations thereof. Mixed oxides that may be used in theactivator-support of the present techniques may include, for example,mixed oxides of any combination of Al, B, Be, Bi, Cd, Co, Cr, Cu, Fe,Ga, La, Mn, Mo, Ni, P, Sb, Si, Sn, Sr, Th, Ti, V, W, Y, Zn, Zr, and thelike. Examples of mixed oxides that may be used in the activator-supportof the present techniques may also include silica-alumina,silica-titania, silica-zirconia, zeolites, many clay minerals, pillaredclays, alumina-titania, alumina-zirconia, aluminophosphate, and thelike.

The electron-withdrawing component used to treat the oxide may be anycomponent that increases the Lewis or Brønsted acidity of the solidoxide upon treatment. In one embodiment, the electron-withdrawingcomponent is typically an electron-withdrawing anion derived from asalt, an acid, or other compound such as a volatile organic compoundthat can serve as a source or precursor for that anion. Examples ofelectron-withdrawing anions include, for example, fluoride, chloride,bromide, iodide, phosphate, trifluoromethane sulfonate (triflate),bisulfate, sulfate, fluoroborate, fluorosulfate, trifluoroacetate,phosphate, fluorophosphate, fluorozirconate, fluorosilicate,fluorotitanate, permanganate, substituted or unsubstitutedalkanesulfonate, substituted or unsubstituted arenesulfonate,substituted or unsubstituted alkylsulfate, and the like, including anymixtures and combinations thereof. In addition, other ionic or non-ioniccompounds that serve as sources for these electron-withdrawing anionsmay also be used in the present techniques. In certain embodiments, thechemically-treated solid oxide may be a sulfated solid oxide, such as asulfated silica or a sulfated alumina.

3. Organoaluminum Compounds

As noted above, the metallocene catalyst systems of the presentembodiments may include the metallocene, a solid oxideactivator-support, and, in some embodiments, an organoaluminum compound.The organoaluminum compound may be omitted when it is not needed toimpart catalytic activity to the catalyst composition. In certainembodiments, the organoaluminum compound may be considered to be thecocatalyst 80.

Organoaluminum compounds that may be used in the catalyst systemsinclude, for example, compounds with the formula:Al(X⁷)_(n)(X⁸)_(3-n),wherein X⁷ may be a hydrocarbyl having from 1 to about 20 carbon atoms;X⁸ may be alkoxide or aryloxide, any of which having from 1 to about 20carbon atoms, halide, or hydride; and n may be a number from 1 to 3,inclusive. In various embodiments, X⁷ may be an alkyl having from 1 toabout 10 carbon atoms. Moieties used for X⁷ may include, for example,methyl, ethyl, propyl, butyl, sec-butyl, isobutyl, 1-hexyl, 2-hexyl,3-hexyl, isohexyl, heptyl, or octyl, and the like. In other embodiments,X⁸ may be independently fluoride, chloride, bromide, methoxide,ethoxide, or hydride. In yet another embodiment, X⁸ may be chloride.

In the formula Al(X⁷)_(n)(X⁸)_(3-n), n may be a number from 1 to 3inclusive, and in an exemplary embodiment, n is 3. The value of n is notrestricted to an integer, therefore this formula may includesesquihalide compounds, other organoaluminum cluster compounds, and thelike.

Generally, organoaluminum compounds that may be used in the catalystsystems may include trialkylaluminum compounds, dialkylaluminium halidecompounds, dialkylaluminum alkoxide compounds, dialkylaluminum hydridecompounds, and combinations thereof. Examples of such organoaluminumcompounds include trimethylaluminum, triethylaluminum (TEA),tripropylaluminum, tributylaluminum, tri-n-butylaluminum (TNBA),triisobutylaluminum (TIBA), trihexylaluminum, triisohexylaluminum,trioctylaluminum, diethylaluminum ethoxide, diisobutylaluminum hydride,or diethylaluminum chloride, or any combination thereof. If theparticular alkyl isomer is not specified, the compound may encompass allisomers that can arise from a particular specified alkyl group.

As noted above, in certain embodiments, the metallocene catalyst systemmay include or be used in conjunction with aluminoxane, boratecompounds, MgCl₂, or any combination thereof. In particular, compoundssuch as aluminoxanes, organoboron compounds, ionizing ionic compounds,or any combination thereof, may be used as the cocatalyst 80 with thecatalyst 78, either in the presence or absence of the activator supportdiscussed above. Additionally, such cocatalysts may be used with themetallocene, either in the presence or absence of an organoaluminumcompound. Thus, the organoaluminum cocatalyst compound discussed abovemay be optional, for instance when a ligand on the metallocene is ahydrocarbyl group, H, or BH₄; when the activator includes anorganoaluminoxane compound; or when both these conditions are present.However, the catalyst compositions of the present techniques may beactive in the substantial absence of cocatalysts such as aluminoxanes,organoboron compounds, ionizing ionic compounds, or any combinationthereof. It is also within the scope of the current techniques to use analuminoxane in combination with a trialkylaluminum, such as disclosed inU.S. Pat. No. 4,794,096, which is herein incorporated by reference inits entirety for all purposes.

4. Organoaluminoxane Compounds

By way of example, the catalyst composition may not require an acidicactivator-support such as a chemically-treated solid oxide to weaken thebonds between the metal and the X⁴ or X⁵ ligands, as theorganoaluminoxane may perform this function, or may replace the X⁴ or X⁵ligands with more active species. The catalyst composition may also notrequire an organoaluminum compound. Thus, any metallocene compoundspresented herein may be combined with any of the aluminoxanes presentedherein, or any combination of aluminoxanes presented herein, to formcatalyst compositions of the present techniques. The organoaluminoxanesdescribed herein may be considered to be a cocatalyst. Further, anymetallocene compounds presented herein may be combined with anyaluminoxane or combination of aluminoxanes, and an activator-supportsuch as, for example, a layered mineral, an ion-exchangeableactivator-support, an organoboron compound or an organoborate compound,to form a catalyst composition of the present techniques.

Aluminoxanes may be referred to as poly(hydrocarbyl aluminum oxides) ororganoaluminoxanes. The other catalyst components may be contacted withthe aluminoxane in a saturated hydrocarbon compound solvent, though anysolvent which is substantially inert to the reactants, intermediates,and products of the activation step may be used. The catalystcomposition formed in this manner may be collected by any methodincluding, but not limited to filtration, or the catalyst compositionmay be introduced into the polymerization reactor without beingisolated.

The aluminoxane compound of the present techniques may be an oligomericaluminum compound, wherein the aluminoxane compound may include linearstructures, cyclic, or cage structures, or mixtures of all three. Cyclicaluminoxane compounds having the formula:

whereinR may be a linear or branched alkyl having from 1 to 10 carbon atoms,and n may be an integer from 3 to about 10 may be encompassed by thepresent techniques. The (AlRO)_(n) moiety shown here also constitutesthe repeating unit in a linear aluminoxane. Thus, linear aluminoxaneshaving the formula:

whereinR may be a linear or branched alkyl having from 1 to 10 carbon atoms,and n may be an integer from 1 to about 50, are also encompassed by thepresent techniques.

Further, useful aluminoxanes may also have cage structures of theformula R^(t) _(5m+α)R^(b) _(m−α)Al_(4m)O_(3m), wherein m may be 3 or 4and α is equal to n_(Al(3))−n_(O(2))+n_(O(4)). In this structuren_(Al(3)) is the number of three coordinate aluminum atoms, n_(O(2)) isthe number of two coordinate oxygen atoms, and n_(O(4)) is the number of4 coordinate oxygen atoms. R^(t) represents a terminal alkyl group andR^(b) represents a bridging alkyl group, either of which may have from 1to 10 carbon atoms.

Thus, aluminoxanes may be represented generally by formulas such as(R—Al—O)_(n), R(R—Al—O)_(n)AlR₂, and the like, wherein the R group maybe a linear or branched C₁-C₆ alkyl such as methyl, ethyl, propyl,butyl, pentyl, or hexyl, and n may represent an integer from 1 to about50. The aluminoxane compounds of the present techniques may include, forexample, methylaluminoxane (MAO), ethylaluminoxane, n-propylaluminoxane,iso-propylaluminoxane, n-butylaluminoxane, t-butylaluminoxane,sec-butylaluminoxane, iso-butylaluminoxane, 1-pentylaluminoxane,2-pentylaluminoxane, 3-pentylaluminoxane, iso-pentylaluminoxane,neopentylaluminoxane, or combinations thereof.

While organoaluminoxanes with different types of R groups areencompassed by the present techniques, methyl aluminoxane (MAO), ethylaluminoxane, or isobutyl aluminoxane may also be used as cocatalysts inthe compositions of the present techniques. These aluminoxanes may beprepared from trimethylaluminum, triethylaluminum, ortriisobutylaluminum, respectively, and may be referred to as poly(methylaluminum oxide), poly(ethyl aluminum oxide), and poly(isobutyl aluminumoxide), respectively. The present techniques encompass many values of nin the aluminoxane formulas (R—Al—O)_(n) and R(R—Al—O)_(n)AlR₂. Inexemplary aluminoxanes, n may be at least about 3. However, dependingupon how the organoaluminoxane may be prepared, stored, and used, thevalue of n may be variable within a single sample of aluminoxane, andsuch combinations of organoaluminoxanes are encompassed by the methodsand compositions of the present techniques.

Organoaluminoxanes may be prepared by various procedures which areavailable. Examples of organoaluminoxane preparations are disclosed inU.S. Pat. Nos. 3,242,099 and 4,808,561, each of which is incorporated byreference herein in its entirety for all purposes. One example of how analuminoxane may be prepared is as follows. Water may be dissolved in aninert organic solvent and then reacted with an aluminum alkyl compoundsuch as AlR₃ to form the desired organoaluminoxane compound. While notintending to be bound by this statement, it is believed that thissynthetic method can afford a mixture of both linear and cyclic(R—Al—O)_(n) aluminoxane species, both of which are encompassed by thepresent techniques. Alternatively, organoaluminoxanes may be prepared byreacting an aluminum alkyl compound such as AlR₃ with a hydrated salt,such as hydrated copper sulfate, in an inert organic solvent.

5. Organoboron Compounds

The present disclosure is also intended to encompass catalystcompositions that use organoboron or organoborate compounds. Anymetallocene compound presented herein may be combined with any of theorganoboron or organoborate cocatalysts presented herein, or anycombination of organoboron or organoborate cocatalysts presented herein.This composition may include a component that provides an activatableligand such as an alkyl or hydride ligand to the metallocene, when themetallocene compound does not already include such a ligand, such as anorganoaluminum compound. Further, any metallocene compounds presentedherein may be combined with: any an organoboron or organoboratecocatalyst; an organoaluminum compound; optionally, an aluminoxane; andoptionally, an activator-support; to form a catalyst composition of thepresent techniques.

The term “organoboron” compound may be used to refer to neutral boroncompounds, borate salts, or combinations thereof. For example, theorganoboron compounds in various embodiments may be a fluoroorgano boroncompound, a fluoroorgano borate compound, or a combination thereof. Anyfluoroorgano boron or fluoroorgano borate compound may be utilized. Theterm fluoroorgano boron has its usual meaning to refer to neutralcompounds of the form BY₃. The term fluoroorgano borate compound alsohas its usual meaning to refer to the monoanionic salts of afluoroorgano boron compound of the form [cation]⁺[BY₄]⁻, where Yrepresents a fluorinated organic group. For convenience, fluoroorganoboron and fluoroorgano borate compounds may be referred to collectivelyby organoboron compounds, or by either name as the context requires.

Fluoroorgano borate compounds that may be used as cocatalysts in thepresent techniques include, for example, fluorinated aryl borates suchas, N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate,triphenylcarbenium tetrakis(pentafluorophenyl)borate, lithiumtetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis[3,5-bis(trifluoro-methyl)phenyl]borate, triphenylcarbeniumtetrakis[3,5-bis(trifluoromethyl)phenyl]borate, and the like, includingmixtures thereof. Examples of fluoroorgano boron compounds that may beused as cocatalysts in the present techniques include, for example,tris(pentafluorophenyl)boron, tris[3,5-bis(trifluoromethyl)phenyl]boron,and the like, including mixtures thereof.

Although not intending to be bound by the following theory, theseexamples of fluoroorgano borate and fluoroorgano boron compounds, andrelated compounds, are thought to form “weakly-coordinating” anions whencombined with organometal compounds, as disclosed in U.S. Pat. No.5,919,983, which is herein incorporated by reference in its entiretyherein.

6. Ionizing Ionic Compounds

Embodiments of the present techniques may include a catalyst compositionas presented herein, including an optional ionizing ionic compound inaddition to other components. Examples of ionizing ionic compounds aredisclosed in U.S. Pat. Nos. 5,576,259 and 5,807,938 which are hereinincorporated by reference in their entirety for all purposes.

An ionizing ionic compound is an ionic compound which can function toenhance activity and/or productivity of the catalyst composition. Whilenot intending to be bound by theory, it is believed that the ionizingionic compound may be capable of reacting with the metallocene compoundand converting the metallocene into a cationic metallocene compound.Again, while not intending to be bound by theory, it is believed thatthe ionizing ionic compound can function as an ionizing compound bycompletely or partially extracting an anionic ligand, possibly anon-η⁵-alkadienyl ligand, such as X³ or X⁴, from the metallocene.However, the ionizing ionic compound is an activator regardless ofwhether it is ionizes the metallocene, abstracts an X⁴ or X⁵ ligand in afashion as to form an ion pair, weakens the metal-(X⁴) or metal-(X⁵)bond in the metallocene, simply coordinates to an X⁴ or X⁵ ligand, orfollows any other mechanisms by which activation can occur. Further, itis not necessary that the ionizing ionic compound activate themetallocene only. The activation function of the ionizing ionic compoundmay be evident in the enhanced activity and/or productivity of catalystcomposition as a whole, as compared to a catalyst composition containingcatalyst composition that does not include any ionizing ionic compound.

Examples of ionizing ionic compounds may include, for example, suchcompounds as: tri(n-butyl)ammonium tetrakis(p-tolyl)borate,tri(n-butyl)ammonium tetrakis(m-tolyl)borate, tri(n-butyl)ammoniumtetrakis(2,4-dimethylphenyl)borate, tri(n-butyl)ammoniumtetrakis(3,5-dimethylphenyl)borate, tri(n-butyl)ammoniumtetrakis[3,5-bis(trifluoromethyl)phenyl]borate, tri(n-butyl)ammoniumtetrakis(pentafluorophenyl)borate, N,N-dimethylaniliniumtetrakis(p-tolyl)borate, N,N-dimethylanilinium tetrakis(m-tolyl)borate,N,N-dimethylanilinium tetrakis(2,4-dimethylphenyl)borate,N,N-dimethylanilinium tetrakis(3,5-dimethylphenyl)borate,N,N-dimethylanilinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate,N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate,triphenylcarbenium tetrakis(p-tolyl)borate, triphenylcarbeniumtetrakis(m-tolyl)borate, triphenylcarbeniumtetrakis(2,4-dimethylphenyl)borate, triphenylcarbeniumtetrakis(3,5-dimethylphenyl)borate, triphenylcarbeniumtetrakis[3,5-bis(trifluoromethyl)phenyl]borate, triphenylcarbeniumtetrakis(pentafluorophenyl)borate, tropylium tetrakis(p-tolyl)borate,tropylium tetrakis(m-tolyl)borate, tropyliumtetrakis(2,4-dimethylphenyl)borate, tropyliumtetrakis(3,5-dimethylphenyl)borate, tropyliumtetrakis[3,5-bis(trifluoromethyl)phenyl]borate, tropyliumtetrakis(pentafluorophenyl)borate, lithiumtetrakis(pentafluorophenyl)borate, lithium tetrakis(phenyl)borate,lithium tetrakis(p-tolyl)borate, lithium tetrakis(m-tolyl)borate,lithium tetrakis(2,4-dimethylphenyl)borate, lithiumtetrakis(3,5-dimethylphenyl)borate, lithium tetrafluoroborate, sodiumtetrakis(pentafluorophenyl)borate, sodium tetrakis(phenyl)borate, sodiumtetrakis(p-tolyl)borate, sodium tetrakis(m-tolyl)borate, sodiumtetrakis(2,4-dimethylphenyl)borate, sodiumtetrakis(3,5-dimethylphenyl)borate, sodium tetrafluoroborate, potassiumtetrakis(pentafluorophenyl)borate, potassium tetrakis(phenyl)borate,potassium tetrakis(p-tolyl)borate, potassium tetrakis(m-tolyl)borate,potassium tetrakis(2,4-dimethylphenyl)borate, potassiumtetrakis(3,5-dimethylphenyl)borate, potassium tetrafluoroborate,triphenylcarbenium tetrakis(p-tolyl)aluminate, triphenylcarbeniumtetrakis(m-tolyl)-aluminate, triphenylcarbeniumtetrakis(2,4-dimethylphenyl)aluminate, triphenylcarbeniumtetrakis(3,5-dimethylphenyl)aluminate, triphenylcarbeniumtetrakis(pentafluorophenyl)aluminate, tropyliumtetrakis(p-tolyl)aluminate, tropylium tetrakis(m-tolyl)aluminate,tropylium tetrakis(2,4-dimethylphenyl)aluminate, tropyliumtetrakis(3,5-dimethylphenyl)aluminate, tropyliumtetrakis(pentafluorophenyl)aluminate, lithiumtetrakis(pentafluorophenyl)aluminate, lithium tetrakis(phenyl)aluminate,lithium tetrakis(p-tolyl)aluminate, lithium tetrakis(m-tolyl)aluminate,lithium tetrakis(2,4-dimethylphenyl)aluminate, lithiumtetrakis(3,5-dimethylphenyl)aluminate, lithium tetrafluoroaluminate,sodium tetrakis(pentafluorophenyl)aluminate, sodiumtetrakis(phenyl)aluminate, sodium tetrakis(p-tolyl)aluminate, sodiumtetrakis(m-tolyl)aluminate, sodiumtetrakis(2,4-dimethylphenyl)aluminate, sodiumtetrakis(3,5-dimethylphenyl)aluminate, sodium tetrafluoroaluminate,potassium tetrakis(pentafluorophenyl)aluminate, potassiumtetrakis(phenyl)aluminate, potassium tetrakis(p-tolyl)aluminate,potassium tetrakis(m-tolyl)-aluminate, potassiumtetrakis(2,4-dimethylphenyl)aluminate, potassiumtetrakis(3,5-dimethylphenyl)aluminate, potassium tetrafluoroaluminate,triphenylcarbenium tris(2,2′,2″-nonafluorobiphenyl)fluoroaluminate,silver tetrakis(1,1,1,3,3,3-hexafluoroisopropanolato)aluminate, orsilver tetrakis(perfluoro-t-butoxy)aluminate, or any combinationthereof.

As noted above, a precontacted mixture of the fouling reduction agent 16and the catalyst 78 (and any cocatalyst 80) may be produced before themonomer 84 and/or comonomer 86 are allowed to interact with the catalystcomposition (e.g., in a reaction/polymerization zone). In this way, themonomer 84 and/or comonomer 86 may be contacted with the precontactedmixture of the fouling reduction agent 16 and the catalyst 78 (and anycocatalyst 80) before introduction into the reactor 60 (e.g., in aprecontactor), after the catalyst composition is introduced into thereactor 60, or any combination thereof. Again, in certain embodiments,precontacting the monomer 84 and/or comonomer 86 with the precontactedmixture of the fouling reduction agent 16 and the catalyst 78 (and anycocatalyst 80) may enable enhanced catalyst activity and/orproductivity.

7. Example Catalyst Compositions

In accordance with present embodiments, as noted above, precontactingthe fouling reduction agent 16, the catalyst 78, and, in someembodiments, one or more cocatalysts and/or activators may produce acatalyst composition that is better able to tolerate the presence ofwater compared to a catalyst composition that does not include thefouling reduction agent 16. By way of specific example, in someembodiments, a catalyst composition includes a contact product ofcontact components including a metallocene, an agent including anammonium salt (e.g., a tetraalkylammonium salt, an ionic liquid, apolymer having the ammonium salt, or any combination thereof), anorganoaluminum and/or organoaluminoxane, and a solid oxideactivator-support. In certain of these embodiments, the catalystcomposition includes the contact product of contact components includinga metallocene catalyst, a tetraalkylammonium salt, an organoaluminum,and a chemically treated solid oxide activator-support (e.g., an SSA).In further embodiments, the catalyst composition includes the contactproduct of contact components including a metallocene catalyst, atetraalkylammonium halide salt, a trialkylaluminum and/or MAO, and achemically treated solid oxide activator-support.

In still further embodiments, the catalyst composition includes thecontact product of contact components including an ansa-metallocenecatalyst, a tetra(n-butyl)ammonium halide salt and/or atetra(n-dodecyl)ammonium halide salt, a trialkylaluminum and/or MAO, anda fluorided or sulfated solid oxide activator-support. In someembodiments of the catalyst compositions above, the contact componentsare substantially free of monomers, such as α-olefins. In otherembodiments, the contact components further include α-olefins such asethylene, 1-hexene, or a combination thereof.

IV. Preparation of the Catalyst Composition

The present disclosure encompasses a catalyst composition (e.g., theprecontacted mixture 22) prepared by a method that includes contactingthe olefin polymerization catalyst 78 and the fouling reduction agent16, as presented herein. The method presented herein encompasses anyseries of contacting steps that allows the catalyst 78 or a catalystsystem formed using the catalyst 78 to be contacted with the foulingreduction agent 16, including any order of contacting the foulingreduction agent 16 with any components used to generate the catalystsystem. While not intending to be limiting, examples of contacting stepsmay be exemplified using a metallocene, a treated solid oxideactivator-support, and an organoaluminum, and contacting thesecomponents with the fouling reduction agent 16. These steps mayencompass any number of precontacting and postcontacting steps, and mayfurther encompass using the monomer 84 and/or the comonomer 86 as acontact component at certain steps before or after the fouling reductionagent 16 is present. Examples of methods to prepare the catalystcomposition of the present disclosure are discussed below.

FIG. 3 illustrates an example scheme 150 for producing catalystcompositions in accordance with the present disclosure. By way ofexample, the scheme 150 may be performed by the control system 90 incombination with the various flow control features depicted in FIG. 2.However, in some embodiments, a human operator may perform certain ofthese tasks, either alone or in combination with the control system 90.However, embodiments in which the entire scheme 150 is automated arepresently contemplated.

As set forth above, the present disclosure encompasses forming catalystcompositions by contacting the fouling reduction agent 16 with thecatalyst 78 or a catalyst system incorporating the catalyst 78. Asdepicted in FIG. 3, a number of components may be provided to one ormore precontactors in order to produce the catalyst composition,including the fouling reduction agent 16 (which can include multipleagents), the catalyst 78, the diluent 82, the cocatalyst(s)/activator(s)80 (which may include multiple components that may be individuallyconsidered to be activators or cocatalysts), and, in some situations,the monomer 84 and/or comonomer 86.

The scheme 150 includes the controlled delivery (block 152) of any oneor a combination of these components to one or more precontactors atspecific times, which causes one or more contact products to be produced(block 154). For example, multiple contact products may be formed byprecontacting a first set of components followed by precontacting thefirst set with a second set of components. Once formed, the contactproducts may produce a catalyst composition, which may be controllablydelivered (block 156) to a polymerization reactor as generally discussedabove.

A. Precontacting the Catalyst and Fouling Reduction Agent

As discussed above, the fouling reduction agent 16 and the catalyst 78or a catalyst system produced using the catalyst 78, may enhance thetolerance of the catalyst system to various undesirable components, suchas water. The fouling reduction agent 16 may, for example, beprecontacted with the catalyst 78 before or after the catalyst 78 hasbeen activated or contacted with a cocatalyst. In other embodiments, theprecontacting of the catalyst 78 and the fouling reduction agent 16 maybe performed as the catalyst 78 is being activated or has otherwisecontacted a cocatalyst. Precontacting in accordance with presentembodiments may be carried out in any suitable equipment, such as tanks,stirred mix tanks, various static mixing devices, a tube, a flask, avessel of any type, or the polymerization reactor before polymerizationconditions are initiated, or any combination thereof. Indeed, any orderof precontacting of any of the components noted above is presentlycontemplated.

Generally, the fouling reduction agent 16 may be precontacted with thecatalyst (e.g., the metallocene compound), or any other precontactedmixture having the catalyst, for any appropriate amount of time. Theappropriate amount of time for precontacting may be determined based onpolymerization scale, precontact conditions (e.g., temperature,pressure), catalyst requirements (e.g., throughput), polymerizationconditions, and the particular components used. By way of example, theprecontact time between the fouling reduction agent 16 and themetallocene may be on the order of seconds, such as between 1 second and50 seconds, between 1 second and 30 seconds, or between 5 seconds and 20seconds. Alternatively, the precontact time between the foulingreduction agent 16 and the metallocene may be on the order of minutes,such as between 1 minute and 50 minutes, between 1 minute and 30minutes, between 1 minute and 15 minutes, or between 1 minute and 5minutes. Precontact times greater than 1 hour are also presentlycontemplated, such as precontact times of between 1 hour and 24 hours.

In some embodiments, a metallocene catalyst (which may or may not havebeen precontacted with an activator-support) may be first contacted withan organoaluminum for a first period of time. The first period of timefor contact, the first precontact time, between the metallocene and theorganoaluminum may be any appropriate contacting time, such as a rangein time from about 1 second to about 24 hours, from about 0.1 to about 1hour, or from about 10 minutes to about 30 minutes. In some embodiments,a monomer, not necessarily the monomer to be polymerized, may be addedfor additional activation of the catalyst. After the organoaluminum andthe metallocene have been precontacted for the first period of time, afirst contact product may be produced. The first contact product maythen be contacted with the fouling reduction agent 16 (e.g., atetraalkylammonium salt) for a second period of time, a second contacttime, to produce a second contact product. The second contact time maybe any appropriate contact time, such as from about 1 second to about 24hours, between 1 second and 50 seconds, between 1 second and 30 seconds,or between 5 seconds and 20 seconds, alternatively between 1 minute and50 minutes, between 1 minute and 30 minutes, between 1 minute and 15minutes, or between 1 minute and 5 minutes, alternatively between 1 hourand 24 hours.

In some embodiments (e.g., when the metallocene has not yet contacted asolid oxide), the second contact product may be contacted with a solidoxide activator-support. The resulting composition may be, in someembodiments, termed a postcontacted mixture. The postcontacted mixturemay be allowed to remain in contact for a third period of time, thepostcontact time, prior to being used in the polymerization process.Postcontact times between the solid oxide activator-support and thesecond precontacted mixture may range in time from about 1 minute toabout 24 hours, from 0.1 hours to about 1 hour, or from about 10 minutesto about 30 minutes.

Further processing may be performed to adsorb one or more of thecatalyst composition components onto the solid oxide. However, suchadsorption is not required. For example, the postcontacted mixture maybe heated at a temperature and for a time sufficient to allowadsorption, impregnation, or interaction of precontacted mixture and thesolid oxide activator-support, such that a portion of the components ofthe precontacted mixture may be immobilized, adsorbed, or depositedthereon. For example, the postcontacted mixture may be heated frombetween about 0° F. to about 150° F. (about −18° C. to about 66° C.), orfrom between about 40° F. to about 95° F. (about 7° C. to about 35° C.).

The various catalyst components (for example, metallocene,activator-support, organoaluminum, and tetraalkylammonium salt) may beprecontacted in any order, and not necessarily the order noted above.The precontacting of these components may be a continuous process, inwhich the precontacted product (e.g., the precontacted mixture 22) maybe fed continuously to the reactor (e.g., loop slurry reactor 60), ormay be performed in a stepwise or batchwise process in which one or morebatches of precontacted product(s) may be used to make a catalystcomposition. Batches of the catalyst composition may be added to thereactor once or at various intervals.

The overall precontacting process may be carried out over a time periodthat may range from a few seconds to as much as several days, or longer.For example, the continuous precontacting process may last from about 1second to about 1 hour, from about 10 seconds to about 45 minutes, orfrom about 1 minute to about 30 minutes.

B. Multiple Precontacting Steps

The precontacting process may be carried out in multiple steps in whichmultiple mixtures are prepared, each including a different set ofcatalyst composition components. For example, at least two catalystcomposition components (e.g., the metallocene and the organoaluminum)may be contacted forming a first mixture, followed by contacting thefirst mixture with another catalyst composition component (e.g., thefouling reduction agent 16) forming a second mixture, and so forth. Forexample, a first mixture of two catalyst components may be formed in afirst vessel, a second mixture including the first mixture plus oneadditional catalyst composition component may be formed in the firstvessel or in a second vessel, which may be placed downstream of thefirst vessel. As another example, the fouling reduction agent 16 may befirst contacted with a cocatalyst (e.g., organoaluminum,organoaluminoxane) and/or an activator (e.g., solid oxideactivator-support) to form a first mixture. This first mixture may thenbe added to a second mixture that includes the metallocene.

In this way, one or more of the catalyst composition components may besplit and used in different precontacting treatments. For example, partof a catalyst composition component may be fed into a firstprecontacting vessel for precontacting with another catalyst compositioncomponent, while the remainder of that same catalyst compositioncomponent may be fed into a second precontacting vessel forprecontacting with another catalyst composition component, or may be feddirectly into the reactor, or a combination thereof. By way ofnon-limiting example, a catalyst composition of the present techniquesmay be prepared by contacting 1-hexene, an ansa-metallocene, and asulfated alumina activator for a first contact time to produce a firstcontacted mixture, contacting triisobutylaluminum withtetra(n-butyl)ammonium chloride or tetra(n-dodecyl)ammonium chloride forat a second contact time to produce a second contacted mixture, followedby contacting the second contacted mixture with the first contactedmixture for at least about 1 second up to about one hour to form theactive catalyst composition. Example contact times are discussed infurther detail below.

While the catalyst compositions produced in accordance with presentembodiments may benefit from precontacting the fouling reduction agent16 with the catalyst 78 before introducing the catalyst composition intothe reactor, in some embodiments, neither a precontacting step nor apostcontacting step may be required for the present techniques. Forinstance, the fouling reduction agent 16 and other catalyst compositioncomponents (e.g., those depicted in FIG. 3) may be injected as separatestreams into the reactor, albeit in sufficient proximity so as to ensureappropriate contacting within the polymerization reactor beforesubstantial polymerization by the catalyst has occurred. In oneembodiment, the fouling reduction agent 16, and in particular atetraalkylammonium salt, may be added at any time to the reactor,regardless of the introduction time of the catalyst system into thereactor and regardless of whether the catalyst system has begun thepolymerization process.

C. Component Ratios for Catalyst Composition

In embodiments of the present techniques, the molar ratio of the foulingreduction agent 16 to the catalyst 78 (e.g., metallocene) compound maybe from about 1:1 to about 1:10,000 (e.g., about 1:2, 1:5, 1:20, 1:50,1:200, 1:500, 1:2000, 1:5000, 1:8000, etc.), from about 1:1 to about1:1,000, or from about 1:1 to about 1:100. These molar ratios reflectthe ratio of the fouling reduction agent 16 to metal in the catalyst 78(e.g., the metal of the metallocene compound) in the catalystcomposition (e.g., the precontacted mixture 22). Alternativelyrepresented and in further embodiments, the mol ratio of the foulingreduction agent 16 to the metallocene compound may be between 0.01 to 1and 1:1, between 0.02 to 1 and 0.2 to 1, between 0.05 to 1 and 0.5 to 1,or between 0.1 to 1 and 0.8 to 1. It should be noted that in certaincircumstances, such as in continuous processes, the mol ratio of thefouling reduction agent 16 to the metallocene compound may be maintainedbased on their relative amounts in the precontactor, or based on theirrelative amounts in the reactor, or both. By way of specific example, inone non-limiting embodiment, an approximate ratio of between 0.1 and 0.2mol tetra(n-dodecyl)ammonium chloride (e.g., between approximately 0.10mol and 0.15 mol) to 1 mol metallocene may be sufficient, and anapproximate ratio of between 0.1 and 0.2 mol tetra(n-butyl)ammoniumchloride (e.g., between approximately 0.14 and 0.18 mol) to 1 molmetallocene may be sufficient to mitigate fouling while also enabling asubstantial maintenance of catalyst activity.

Excess fouling reduction agent 16 to catalyst is also presentlycontemplated, although higher catalyst activity and/orproductivity/productivity may be obtained at molar ratios of less than1:1 fouling reduction agent 16 to catalyst 78. Thus, as an alternative,the molar ratio of the catalyst 78 (e.g., metallocene) compound to thefouling reduction agent 16 may be from about 1:1 to about 1:10,000(e.g., about 1:2, 1:5, 1:20, 1:50, 1:200, 1:500, 1:2000, 1:5000, 1:8000,etc.), from about 1:1 to about 1:1,000, or from about 1:1 to about1:100. As above, these molar ratios reflect the ratio of metal in thecatalyst 78 (e.g., the metal of the metallocene compound) to the foulingreduction agent 16 in the catalyst composition (e.g., the precontactedmixture 22).

In embodiments of the present techniques, the molar ratio of thecatalyst 78 (e.g., metallocene compound) to the cocatalyst 80 (e.g.,organoaluminum compound, and/or organoaluminoxane compound, and/ororganoboron compound, and/or ionizing compound) may be any suitableratio. Typical ranges are from about 1:1 to about 1:10,000 (e.g., about1:2, 1:5, 1:20, 1:50, 1:200, 1:500, 1:2000, 1:5000, 1:8000, etc.), fromabout 1:1 to about 1:1,000, or from about 1:1 to about 1:100. Thesemolar ratios reflect the ratio of metal in the catalyst 78 (e.g., themetal of the metallocene compound) to the total amount of organoaluminumand/or organoaluminoxane compound in all mixtures, such as in thecatalyst composition. The weight ratio of the catalyst 78 (e.g.,metallocene compound) to solid oxide activator-support may also be anysuitable amount. Typical molar ratios are from about 1:1 to about1:1,000,000 (e.g., 1:2, 1:10, 1:5,000, 1:100,000, etc.), from about 1:10to about 1:100,000, or from about 1:20 to about 1:1000 in the catalystcomposition. In embodiments where the catalyst 78 is precontacted with amonomer, the molar ratio of monomer to metallocene compound in theprecontacted mixture may be from about 1:10 to about 100,000:1 (e.g.,1:10, 1:5, 1:1, 5:1, 5000:1, 10,000:1, 50,000:1, etc.), or from about10:1 to about 1,000:1.

V. Properties of the Catalyst Composition in Polymerization Reactions

As noted above, the catalyst compositions formed by contacting acatalyst and fouling reduction agent in accordance with the presenttechnique may be used in any polymerization reaction, includinghomopolymerizations and copolymerizations, such as ethylenehomopolymerizations and ethylene/hexene copolymerizations. The catalystcomposition may be provided to the polymerization reactor continuously,periodically in batches, or only once.

A. Determining Fouling Mitigation and Relative Catalyst Activity and/orProductivity

There may be a number of ways to determine whether a particular material(e.g., a particular ammonium compound) may mitigate fouling (e.g., dueto the presence of water), and the extent to which it is able tomitigate such fouling. For instance, in non-continuous polymerizationruns, fouling mitigation can be qualitatively determined by observingwhether a particular polymerization process in which the particularcomponent is employed results in fouling. In this case, the fouling canbe identified by observing whether there is a buildup of solid polymeron reactor walls or other features of a reactor (e.g., impellers orother mixing devices). The amount of polymer buildup may, in someembodiments, be used to determine the relative fouling mitigationability between different components or different catalyst compositions,such that a first fouling reduction agent may have better foulingmitigation ability compared to a second fouling reduction agent when thepolymerization run in which the first fouling reduction agent isemployed results in less polymer buildup than a process in which thesecond fouling reduction agent is employed.

In both non-continuous and continuous polymerization runs, foulingmitigation can also be qualitatively and, in certain embodiments,quantitatively determined based on the observation of variousoperational parameters of the reactor. For example, fouling may beindicated by deviations from the set reaction temperature or increaseddemand on a coolant system to maintain the set temperature value of thereactor, increased motor load as a pump or other mixing device attemptsto maintain a velocity within the reactor sufficient to keep the polymerand catalyst particles suspended in the diluent, or attempts tocompensate for restriction or obstruction of a flow path. Similarly, ahigh pressure differential may be observed at a pump and may indicatethe presence of a foul. Thus, substantially constant reactiontemperatures, substantially constant pump load (or other load for amixing device), substantially constant pressure differentials,substantially constant flow rates, and so forth, may be indications ofthe ability to mitigate fouling.

Because these monitored parameters are typically associated with values,such as temperatures, pressures, loads, and so forth, it may be possibleto quantify the degree to which a particular component may mitigatefouling. Further, it may be possible to mitigate fouling in real-time(e.g., during a polymerization run) by observing these parameters andmaking adjustments to feedstocks accordingly. For example, the controlsystem 90 of FIG. 2 may monitor operational parameters of the loopslurry reactor 60 and, in response to fouling indicators, may increase aconcentration of the fouling reduction agent 16 relative to the catalyst78 in the precontacted mixture 22, in the reactor 60, or both.

The degree of fouling mitigation ability may be quantified, at least tosome extent, by determining the stability of these measured parameters(e.g., the stability of the reaction temperature, the pressuredifferential across various pumps, the flow rates through the reactor,or any combination thereof) relative to similar types of values observedin other polymerization runs where fouling has occurred, and relative toother polymerization runs where other components that may have similareffects on the polymerization process are employed. In this way,potential fouling reduction agents and/or catalyst compositions may bedirectly compared to one another such that a relative and/or absolutedegree or scale may be generated for different potential foulingreduction agents. Thus, each potential fouling reduction agent may beassociated with a value or some other indication representing theability of the particular agent to mitigate fouling for a particulartype of polymerization under a particular set of conditions.

While a potential fouling reduction agent may be able to mitigatefouling to varying degrees, it should be appreciated that other, moredesirable processes in the reaction should not be correspondinglymitigated. Of particular concern is the activity and/or productivity ofthe catalyst 78, and, more particularly, the activity and/orproductivity of the catalyst composition that is generated beforepolymerization is initiated (e.g., by introduction of the catalystcomposition into a reaction zone of the reactor under polymerizationconditions). Generally, it would be most desirable for the foulingreduction agent 16 to completely mitigate fouling while also enablingthe catalyst system to have the same or enhanced activity and/orproductivity as when the fouling reduction agent 16 is not present.However, the present inventors have found that mitigating fouling mustbe balanced with maintaining catalyst activity and/or productivity suchthat acceptable levels of both are achieved. The present inventors havealso identified a particular set of compounds that are surprisinglywell-suited for fouling mitigation while enabling a substantialmaintenance of catalyst activity and/or productivity.

With respect to determining whether a particular compound is able tomaintain catalyst activity and/or productivity, there exist a variety ofmethods used to determine catalyst activity and/or productivity that arewell-known to those skilled in the art, including measuring the kineticsof the polymerization process. However, one method in accordance withpresent embodiments may involve measuring the relative activities and/orproductivities between a catalyst composition where the catalyst 78 isnot precontacted with the fouling reduction agent 16 and a catalystcomposition where the catalyst 78 is precontacted with the foulingreduction agent 16.

The method may include performing a baseline polymerization reaction. Inthe baseline reaction, a non-continuous polymerization reaction isperformed without the potential fouling reduction agent and withoutintentionally introducing any components that would otherwise causefouling (e.g., water). The output of the reaction is then observed. Theobserved/measured outputs may be the quantity of polymer produced,though other outputs such as various properties of the polymer (e.g.,comonomer incorporation, stereochemistry, M_(w) molecular weight, M_(n)molecular weight, and other physical and mechanical properties) are alsocontemplated. In measuring the amount of polymer produced, a baselineactivity and/or productivity of the catalyst system may be establishedin that an amount of polymer expected from the particular system in aparticular amount of time may be established.

The method may then include performing the same polymerization reaction(e.g., using the same feedstock and the same conditions, and for thesame amount of time) in the presence of water and the fouling reductionagent 16, referred to herein as a test polymerization reaction.Normally, if the fouling reduction agent 16 were not present, a foulwould occur due to the presence of water. For example, the inventorshave observed that the polymerization reaction begins to quickly heat,and a hard foul is then observed. In this type of fouling, solid polymeradheres to reactor walls and various mixing devices. When the foulingreduction agent 16 is present (of suitable type and amount), however,this fouling does not occur. The output of the test polymerizationreaction may then be observed and compared to the output of the baselinepolymerization reaction. For instance, the amount of polymer recoveredfrom the test polymerization reaction within a period of time may becompared to the amount of polymer recovered from the baselinepolymerization reaction within that same period of time to determine therelative activity and/or productivity of the catalyst system between thetwo reactions.

By way of example, if the test polymerization reaction produces anamount of polymer that is within a certain percentage of the amount ofpolymer produced by the baseline polymerization reaction, the foulingreduction agent 16 employed in the test polymerization reaction may bereferred to as maintaining the activity and/or productivity of thecatalyst system to within that percentage of its baseline activityand/or productivity. Thus, a catalyst composition employing the foulingreduction agent 16 that produces 99% of the amount of polymer that wouldbe obtained without the fouling reduction agent 16 (and in the absenceof any fouling condition) would be considered to maintain catalystactivity and/or productivity to within 99% of its baseline activityand/or productivity.

Again, the fouling reduction agent 16 may display these effects in manydifferent types of metallocene catalyst systems, including those thatemploy activator-supports (e.g., acidic solid oxide supports),organoaluminum cocatalysts, organoaluminoxane cocatalysts, and otherionizing components, including those described above. Indeed, as notedabove, surprisingly, tetraalkylammonium salts may exhibit superioroverall performance compared to other compounds when considering themitigation of water-based fouling and catalyst activity and/orproductivity maintenance. It is presently recognized that effectiveranges for tetraalkylammonium halides are generally lower than theranges typically employed for additives that are directly injected intothe reactor, and exhibit better overall performance regardingwater-based fouling mitigation when used in accordance with the presenttechniques.

In terms of weight percentage of a polymerization reaction, exampleweight percentages of the tetraalkylammonium alkyl salts effective forfouling mitigation and catalyst maintenance may be 100 ppm or less,based on the weight of the diluent employed in the reactor. For example,ranges of between 100 ppm and 0.001 ppm may generally be used. By way ofspecific example with respect to commercial-scale polyethyleneproduction, ranges between 10 ppm and 5.0 ppm may be effective atmitigating fouling, but may also reduce catalytic activity and/orproductivity (due to the relative abundance of the ammonium alkylrelative to the catalyst compound). Ranges between 5 ppm and 0.05 ppmmay provide a balance between fouling mitigation and catalytic activityand/or productivity, and ranges between 0.05 ppm and 0.001 ppm, whileeffective for maintaining catalyst activity and/or productivity, may notnecessarily adequately mitigate fouling. It has been identified thatranges between 0.1 ppm and 2.0 ppm, based on the weight of the diluentin the reactor, may be particularly effective for tetraalkylammoniumsalts such as tetra(n-butyl)ammonium chloride andtetra(n-dodecyl)ammonium chloride. By way of non-limiting example,between 0.2 ppm and 0.8 ppm, or between 0.4 ppm and 0.5 ppm may beeffective amounts for tetra(n-dodecyl)ammonium chloride, and between 0.5ppm and 1.1 ppm, or between 0.8 ppm and 1.0 ppm may be effective fortetra(n-butyl)ammonium chloride.

B. Water Tolerance

As noted above, the fouling reduction agent 16 used according to thepresent technique may be particularly useful for mitigating fouling dueto the presence of water, while also maintaining catalyst activityand/or productivity. In this way, the fouling reduction agent 16, whencontacted with the catalyst 78 in preparing a catalyst composition,enables the catalyst composition to be more tolerant to the presence ofwater compared to a catalyst composition that has not been prepared bycontacting the catalyst 78 with the fouling reduction agent 16. Therobustness of the catalyst composition to the presence of water may bedetermined, at least in part, by the amount of fouling reduction agent16 used relative to the catalyst 78, and the amount of water that thecatalyst composition is able to tolerate while still producing anacceptable amount of polymer.

While not being bound by theory, it is believed that in one embodiment,the fouling reduction agent 16, which may include a particular type ofammonium salt, may prevent the metallocene from being solubilized. Thecontact product produced from contacting the fouling reduction agent 16and the metallocene may, in such embodiments, be more tolerant of waterduring polymerization. In one embodiment, water may be blocked frominteracting with the metal center or other coordinated ligands of themetallocene, which is believed to result in fouling. Indeed, as notedabove, it is believed that water can cause a metallocene catalyst todegrade and/or become solubilized.

Thus, the ability of the fouling reduction agent 16 to enable thecatalyst composition to tolerate certain amounts of water may berepresented by, for example, an amount of the particular foulingreduction agent 16 suitable for offsetting a particular amount of waterfor a particular catalyst composition. In one embodiment, this mayinclude representing the tolerance of a particular catalyst composition,formed at least in part by precontacting the fouling reduction agent 16and the catalyst 78, to water relative to the baseline water toleranceof the catalyst composition (i.e., where no fouling reduction agent 16is used). The representation may include denoting a molar or weightratio of the fouling reduction agent 16 to the active component of thecatalyst 78 (e.g., the metallocene structure) and a molar or weightratio of the water to the active component of the catalyst 78, andcomparing the activity and/or productivity of the catalyst systemobtained relative to baseline catalyst activity and/or productivity whenno fouling reduction agent 16 is used and no water is separatelyintroduced. It should be noted that in performing the baselinepolymerization reaction, some water may be present in very small amountsin certain of the feedstocks 14. However, using the same feedstocks 14for both the test and baseline reactions may offset these minorcontaminations.

Regardless of its particular mode of action, certain fouling reductionagents 16, such as those described below, may enable the catalyst systemto tolerate the presence of water in an amount that would otherwisecause a significant foul, while still enabling substantially unchangedcatalyst activity and/or productivity (e.g., to within between 95% and100% of its baseline activity and/or productivity). It is believed,therefore, that the catalyst compositions produced in accordance withpresent embodiments will be able to better tolerate variations in thefeedstocks 14, particularly variations in which water may be introduced.

By way of non-limiting example, in accordance with present embodiments,certain of the fouling reduction agents 16 may maintain the activityand/or productivity of the catalyst to within between 90% and 100% ofits baseline activity and/or productivity while tolerating water in awater to metallocene mol ratio of between approximately 0.0001 mol waterto approximately 1 mol metallocene and approximately 0.01 mol water toapproximately 1 mol metallocene. By way of example, the foulingreduction agents 16 may enable the tolerance of water within a reactor,based on the weight of solvent/diluent in the reactor, in amounts up toabout 5 ppm, such as between 1 and 4 ppm, between 1 and 3 ppm, orbetween 1 and 2 ppm. As an example of what this represents in terms ofthe operation of a polymerization reactor, an incoming feedstock (e.g.,a diluent injection), representing approximately 10% of the totalcontents of the reactor and having approximately 10 ppm water, may betolerated when fouling reduction agents 16, such as tetraalkylammoniumsalts, are used in accordance with the present technique. It should beappreciated that the tolerance of 10 ppm of water in a given feedstockmay represent significant operational flexibility and significantfouling mitigation, where that same 10 ppm of water would otherwisecause a total foul of the reactor.

Again, in some embodiments, the mol ratio of tetraalkylammonium halideto metallocene compound (in the reactor and/or the precontactor) maygenerally be between approximately 0.01 mol tetraalkylammonium halide to1.0 mol of metallocene compound and approximately 1.0 moltetraalkylammonium halide to 1.0 mol of metallocene compound. In orderto mitigate fouling as a result of water while also enabling catalystactivity and/or productivity to be substantially maintained, mol ratiosof between 0.05 to 1 and 0.5 to 1 may be particularly preferred, withbetween approximately 0.1 mol and 0.2 mol fouling reduction agent 16 to1 mol catalyst 78 being particularly effective fortetra(n-dodecyl)ammonium chloride and tetra(n-butyl)ammonium chloride,as discussed in Section IV.C. It has also been found, surprisingly, thatcatalyst activity and/or productivity may be enhanced relative tobaseline activity and/or productivity, and water-based fouling may bemitigated completely when tetra(n-dodecyl)ammonium chloride is used asthe fouling reduction agent 16 when used in these amounts.

Furthermore, it has also been found that certain mol ratios within theseranges may enable catalyst activity and/or productivity maintenance(e.g., to within between 95% and 100% of baseline activity and/orproductivity), while mol ratios outside of these ranges may suffer frominsufficient fouling mitigation and/or catalyst activity and/orproductivity. Indeed, as noted in the examples below, in someembodiments, catalyst activity and/or productivity may be enhancedrelative to baseline. In certain embodiments, this may be due to themitigation of the effect of any contaminant water in the feedstocks 14utilized for the baseline polymerization reaction on the catalystcomposition's baseline activity and/or productivity. In other words, notonly are certain fouling reduction agents 16 able to mitigate the wateradded in the test runs, but certain of these compounds are also able toenhance catalyst activity.

C. Absolute Activity and/or Productivity of the Catalyst Composition

Because the weight of the catalyst 78 may be largely determined by theweight of the solid support on which the active metal of the catalyst 78is supported, the catalyst activity may be represented by themeasurement of grams of polymer (e.g., polyethylene) produced per gramof chemically treated solid oxide per hour (abbreviated gP/(g CTSO·hr)).The catalytic activity and/or productivity of the catalyst compositionof the present disclosure, formed by contacting the catalyst 78 (orcatalyst system produced using the catalyst 78) with the foulingreduction agent 16, may be greater than or equal to about 1000 gP/(gCTSO·hr), greater than or equal to about 3000 gP/(g CTSO·hr), greaterthan or equal to about 6000 gP/(g CTSO·hr), or greater than or equal toabout 9000 gP/(g CTSO·hr). Activity and/or productivity may be measuredunder slurry polymerization conditions using isobutane as the diluent,with a polymerization temperature from about 80° C. to about 100° C.,and an ethylene pressure of about 340 psig to about 550 psig. Thereactor should have substantially no indication of any wall scale,coating or other forms of fouling when making these measurements.

EXAMPLES

The following are real working examples of embodiments of the presenttechnique. While the examples set forth below are demonstrative of theeffects of the present technique, the examples should not be construedas limiting the scope of the present disclosure. In particular, a seriesof polymerization experiments are discussed below, and demonstrate howcertain added fouling reduction agents can significantly reduce oreliminate fouling induced by water during a standard ethylene, hexenecopolymer run in a 1 gallon batch reactor, with stirring performed usinga motor-driven impeller. It should be noted that the various mixing ofcomponents before heating and the introduction of pressurized ethyleneis considered to be representative of the conditions within aprecontactor.

All experiments set forth below were performed using a singlemetallocene, the structure of which is shown below:

This metallocene may be prepared, for example, according to theprocesses outlined in U.S. Pat. No. 7,064,225, which is incorporated byreference herein in its entirety for all purposes. 10 wt % STADIS 450®antistatic additive was obtained from Octel Starreon of Newark, Del.Other reaction components used for the below examples were obtained fromstandard suppliers or using the techniques described in the referencesincorporated above.

The polymerizations described below were run under the same conditionsof temperature (80° C.), pressure of ethylene (450 psig), and no addedhydrogen. 1-hexene was used as comonomer using either 38 g or 40 g, withthe same amount being used between any directly comparative reactions.The metallocene compound was used in an amount of 3 milligrams, andsulfated alumina was used in an amount between 60 mg and 80 mg.Triisobutylaluminum was used as a cocatalyst, and was generallyintroduced by adding approximately 0.6 mL of 15 wt % triisobutylaluminum(TIBA) in hexanes. Standard polymerizations using these reagents,accounting for slight variations in each feedstock, are generallyexpected to produce between 250 grams and 350 grams of polyethylenepolymer.

In the fouling experiments below, water was added with TIBA, and 1 mL ofTIBA was used in these instances. All reactions were performed in 2 Lisobutane (about 5 kg) as the reaction medium, and were run forapproximately 30 minutes. Example 1 was run for only 15 minutes due tofouling. The mitigation of fouling was determined based on anobservation of reaction temperature and the nature of the reactionvessel after the polymerization experiments were performed.

Example 1

To first establish the effect of water on the polymerization reaction, acontrol experiment was run where no fouling reduction agent was added.In this control experiment, the standard polymerization conditions notedabove were used, and 3 microliters of water were added to 1 mL of TIBA.The resulting mixture was then added to the reactor. After approximately15 minutes of polymerization time, the temperature of the reaction wasobserved to be much hotter than a standard run. The reaction was thenterminated, and the reactor was opened. The reactor showed a hard foulwhere polymer totally covered the impeller in a spherical shape, forminga “lollipop” structure. 290 g of PE was ultimately recovered.

Example 2

Having established that the addition of 3 microliters of water was morethan sufficient to cause fouling, subsequent polymerizations wereperformed using 2 microliters. In a first comparative experiment,Example 2, 2 microliters of water was added to 1 mL of TIBA. 0.1 mL of10 wt % STADIS 450® additive was then added to the resulting mixturebefore the introduction of ethylene and before heating the reaction.After 30 minutes, the reaction was opened and it was observed thatfouling was nearly completely mitigated, with less than approximately 1%of the polymer being adhered to the reactor walls or impeller. However,catalyst activity/productivity was somewhat diminished, with 209 g PEbeing recovered. This nevertheless may constitute an unexpected resultin that the STADIS 450® was able to control fouling due to water, whileSTADIS 450® would typically be limited to a use for controlling staticin a polymerization reactor to reduce static-based fouling. The presentinventors have therefore found that the STADIS 450® additive may be usedas a part of a catalyst composition, and may provide control overfouling caused by water (which may affect the catalyst, as opposed toaffecting the polymer as is the case with static).

Examples 3-5

As noted above, tetraalkylammonium salts provide surprisingly goodfouling mitigation ability when used in accordance with the presenttechnique, as displayed by the results discussed below. For Examples3-5, a saturated stock solution of tetra(n-butyl)ammonium chloride intoluene was prepared, and a specific amount of this solution was chargedinto the reactor before each polymerization run. In these experiments, 2microliters of water were added to 1 mL of TIBA, and the resultingmixture was added to the reactor before polymerization was initiated.

In a first run using tetra(n-butyl)ammonium chloride, Example 3, 0.5 mLof the saturated solution was added before the introduction of ethyleneand before heating the reaction. After approximately 30 minutes, thereaction was opened and it was observed that fouling was not completelymitigated, with between approximately 1% and 2% of the polymer beingadhered to the reactor walls and impeller. However, catalystactivity/productivity was substantially maintained, with 256 g PE beingrecovered.

In a second run using tetra(n-butyl)ammonium chloride, Example 4, 1.0 mLof the saturated solution was added before the introduction of ethyleneand before heating the reaction. After approximately 30 minutes, thereaction was opened and it was observed that fouling was totallymitigated in that the reactor walls and impeller were completely free ofpolymer. However, catalyst activity/productivity was significantlyreduced, with less than 100 g PE being recovered.

In a third run using tetra(n-butyl)ammonium chloride, Example 5, 0.6 mLof the saturated solution (representing less than 1 ppmtetra(n-butyl)ammonium chloride, approximately 0.9 ppm based on theweight of the isobutane) was added before the introduction of ethyleneand before heating the reaction. After approximately 30 minutes, thereaction was opened and it was observed that fouling was nearlycompletely mitigated, with less than approximately 1% of the polymerbeing adhered to the reactor walls and the impeller. Catalystactivity/productivity was also completely maintained, with 313 g PEbeing recovered. It should be appreciated that the results aboverelating to the use of tetra(n-butyl)ammonium chloride to control thefouling normally caused by water is quite unexpected. In addition,tetra(n-butyl)ammonium chloride proved to be significantly better thanthe STADIS 450® antistatic additive when considering the combination offouling mitigation and catalyst activity/productivity.

Examples 6 and 7

For Examples 6 and 7, a saturated stock solution oftetra(n-dodecyl)ammonium chloride in toluene was prepared, and aspecific amount of this solution was charged into the reactor beforeeach polymerization run. In these experiments, 2 microliters of waterwere added to 1 mL of TIBA, and the resulting mixture was added to thereactor before polymerization was initiated.

In a first run using tetra(n-dodecyl)ammonium chloride, Example 6, 0.25mL of the saturated solution was added (representing less than 1 ppmtetra(n-dodecyl)ammonium chloride, approximately 0.45 ppm based on theweight of the isobutane) to a mixture of the TIBA, water, themetallocene, and the sulfated alumina. After approximately 30 minutes ofpolymerization, the reaction was opened and it was observed that foulingwas totally mitigated, with no more than a trace amount of polymer beingadhered to the impeller and reactor walls. Catalyst productivity wassubstantially maintained, with 272 g of PE being produced.

In a second run using tetra(n-dodecyl)ammonium chloride, Example 7, 0.25mL of the saturated solution was added (again representing less than 1ppm tetra(n-dodecyl)ammonium chloride, based on the weight of theisobutane) first to a mixture of the TIBA and water, and this resultingmixture was added to the polymerization reactor having a mixture of themetallocene and the sulfated alumina. After approximately 30 minutes ofpolymerization, the reaction was opened and it was observed that foulingwas totally mitigated, with no more than a trace amount of polymer beingadhered to the impeller and reactor walls. Catalyst productivity wastotally maintained and may even be considered to have been enhanced,with 362 g of PE being produced. This is surprising in that a greateramount of polymer was obtained from this reaction than would normally beexpected from a standard polymerization run using no tetraalkylammoniumsalt. Interestingly, the polymerization reaction also appeared tobenefit from precontacting the TIBA/water solution with thetetra(n-dodecyl)ammonium chloride before the TIBA/water solution wasable to contact the catalyst, which could indicate that thetetra(n-dodecyl)ammonium chloride may prevent water from deleteriouslyinteracting with the metallocene compound. As with thetetra(n-butyl)ammonium chloride, tetra(n-dodecyl)ammonium chlorideproved to be significantly better than STADIS 450® antistatic additiveat maintaining catalyst activity/productivity while mitigating fouling.

Additional Description

As discussed above, present embodiments relate to the preparation anduse of a catalyst composition formed by contacting a fouling reductionagent, which may include an ammonium salt (e.g., a tetraalkylammoniumsalt), with a catalyst (e.g., a metallocene catalyst). The followingclauses are offered as further description of the present disclosure,and are intended to cover any and all combinations of the embodimentsset forth above.

Embodiment 1

A method, comprising: introducing a catalyst composition formed within aprecontactor into a polymerization zone of a polymerization reactor; andpolymerizing, within the polymerization zone, an olefin monomer usingthe catalyst composition to produce a polyolefin polymer; and whereinthe catalyst composition formed within the precontactor comprises acontact product of contact components comprising: an olefinpolymerization catalyst; and an agent comprising an ammonium salt,wherein the catalyst composition has a greater catalyst activity in thepresence of water than if no ammonium salt were present.

Embodiment 2

The method of embodiment 1, wherein the olefin polymerization catalystcomprises a metallocene catalyst.

Embodiment 3

The method of any preceding embodiment, wherein the ammonium salt hasthe formula: (R1)(R2)(R3)(R4)N(X), wherein: N is nitrogen; R1, R2, R3,and R4 are independently selected from a hydrogen, an aliphatic grouphaving from 1 to 20 carbons, or an aryl group having from 1 to 20carbons; and X is an anion.

Embodiment 4

The method of any preceding embodiment, wherein the ammonium salt is atetraalkylammonium salt, each alkyl having, independently, from 1 to 20carbons.

Embodiment 5

The method of any preceding embodiment, wherein the ammonium salt is atetraalkylammonium chloride salt, each alkyl having, independently, from4 to 12 carbons.

Embodiment 6

The method of any preceding embodiment, wherein the ammonium salt istetrabutylammonium chloride or tetradodecylammonium chloride.

Embodiment 7

The method of embodiments 1 or 2, wherein the ammonium salt is an ionicliquid at standard temperature and pressure.

Embodiment 8

The method of any preceding embodiment, comprising introducing theolefin polymerization catalyst and the agent separately into theprecontactor such that they first contact within the precontactor.

Embodiment 11

The method of any preceding embodiment, wherein a molar ratio of theammonium salt to the olefin polymerization catalyst is between 0.05 to 1and 0.5 to 1.

Embodiment 12

The method of any preceding embodiment, wherein the polymerizationreactor comprises a loop slurry polymerization reactor.

Embodiment 13

The method of any preceding embodiment, comprising introducing anantistatic agent directly into the polymerization zone.

Embodiment 14

A catalyst composition, comprising: a contact product produced fromcontact components, comprising: an olefin polymerization catalyst; andan ammonium salt having the formula: (R1)(R2)(R3)(R4)N(X), wherein: N isNitrogen; R1, R2, R3, and R4 are independently selected from a hydrogen,an aliphatic group having from 1 to 20 carbons, or an aryl group havingfrom 1 to 20 carbons; and X is an anion.

Embodiment 15

The catalyst composition of embodiment 14, wherein the olefinpolymerization catalyst comprises an organoaluminoxane, a metallocene,or a combination thereof.

Embodiment 16

The catalyst composition of either of embodiments 14 or 15, wherein X isF, Cl, Br, I, a hydroxide, a sulfate, or a phosphate.

Embodiment 17

The catalyst composition of any of embodiments 14-16, wherein each ofR¹, R², R³, and R⁴ are an alkyl group independently having from 1 to 20carbons.

Embodiment 18

The catalyst composition of any of embodiments 14-17, wherein each ofR¹, R², R³, and R⁴ are an alkyl group independently having from 4 to 12carbons.

Embodiment 19

The catalyst composition of any of embodiments 14-18, wherein theammonium salt is tetrabutylammonium chloride or tetradodecylammoniumchloride.

Embodiment 20

The catalyst composition of any of embodiments 14-19, wherein thecontact components comprise a solid super acid (SSA), atrialkylaluminum, or an organoaluminoxane, or any combination thereof.

Embodiment 21

The catalyst composition of any of embodiments 14-20, wherein a molarratio of the ammonium salt to the olefin polymerization catalyst isbetween 0.05 to 1 and 0.5 to 1.

Embodiment 22

A system, comprising a polymerization reactor comprising an olefinmonomer, a catalyst composition, and a diluent, wherein thepolymerization reactor subjects the olefin monomer to polymerizationconditions in the presence of the catalyst composition to produce apolyolefin; a precontactor coupled to an inlet of the polymerizationreactor, wherein the precontactor comprises contact components that formthe catalyst composition, the contact components comprising: an olefinpolymerization catalyst; and an agent comprising an ammonium salt suchthat the catalyst composition has a greater catalyst activity in thepresence of water than if no ammonium salt were present.

Embodiment 23

The system of embodiment 22, wherein the polymerization reactor is aloop slurry reactor.

Embodiment 24

The system of embodiments 22 or 23, comprising a control system havingone or more tangible, non-transitory, machine-readable mediacollectively storing instructions executable by a processor to: monitorconditions within the polymerization reactor for indicators of anincipient reactor foul; adjust an amount of the fouling reduction agentrelative to the olefin polymerization catalyst within the precontactorin response to an indicator of an incipient reactor foul; andcontrollably introduce the catalyst composition into the polymerizationreactor from the precontactor.

While the present disclosure may be susceptible to various modificationsand alternative forms, specific embodiments have been shown by way ofexample in the drawings and tables and have been described in detailherein. However, it should be understood that the embodiments are notintended to be limited to the particular forms disclosed. Rather, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosure as defined by thefollowing appended claims. Further, although individual embodiments arediscussed herein, the disclosure is intended to cover all combinationsof these embodiments.

What is claimed is:
 1. A method, comprising: introducing a catalystcomposition formed within a precontactor into a polymerization zone of apolymerization reactor; and polymerizing, within the polymerizationzone, an olefin monomer using the catalyst composition to produce apolyolefin polymer; wherein the catalyst composition formed within theprecontactor comprises a contact product of contact componentscomprising: an olefin polymerization catalyst; and an agent comprisingan ammonium salt; and wherein the catalyst composition has a greatercatalyst activity in the presence of water than the olefinpolymerization catalyst where the ammonium salt is not present.
 2. Themethod of claim 1, wherein the olefin polymerization catalyst comprisesa metallocene catalyst.
 3. The method of claim 1, wherein the ammoniumsalt has the formula:(R¹)(R²)(R³)(R⁴)N(X), wherein: N is Nitrogen R¹, R², R³, and R⁴ areindependently selected from a hydrogen, an alkyl, branched alkyl,cycloalkyl, aryl, or alkenyl group having from 1 to 20 carbons; and X isan anion.
 4. The method of claim 1, wherein the ammonium salt is atetraalkylammonium salt, each alkyl having, independently, from 1 to 20carbons.
 5. The method of claim 1, wherein the ammonium salt is atetraalkylammonium halide salt, each alkyl having, independently, from 4to 12 carbons.
 6. The method of claim 1, wherein the ammonium salt istetrabutylammonium chloride or tetradodecylammonium chloride.
 7. Themethod of claim 1, wherein the ammonium salt is an ionic liquid atstandard temperature and pressure.
 8. The method of claim 1, comprisingintroducing the olefin polymerization catalyst and the agent separatelyinto the precontactor such that they first contact within theprecontactor.
 9. The method of claim 1, comprising introducing theolefin polymerization catalyst and the agent together as a single streaminto the precontactor such that they first contact before introductioninto the precontactor.
 10. The method of claim 1, wherein a molar ratioof the ammonium salt to the olefin polymerization catalyst is between0.01 to 1.0 and 1 to
 1. 11. The method of claim 1, wherein a molar ratioof the ammonium salt to the olefin polymerization catalyst is between0.05 to 1 and 0.5 to
 1. 12. The method of claim 1, wherein thepolymerization reactor comprises a loop slurry polymerization reactor.13. The method of claim 1, comprising introducing an antistatic agentdirectly into the polymerization zone.
 14. A catalyst compositioncomprising: a contact product produced from contact componentscomprising: an olefin polymerization catalyst; and an ammonium salthaving the formula:(R¹)(R²)(R³)(R⁴)N(X), wherein: N is Nitrogen; R¹, R², R³, and R⁴ areindependently selected from a hydrogen, an aliphatic group having from 1to 20 carbons, or an aryl group having from 1 to 20 carbons; and X is ananion.
 15. The catalyst composition of claim 14, wherein the olefinpolymerization catalyst comprises a metallocene catalyst.
 16. Thecatalyst composition of claim 14, wherein X is F, Cl, Br, I, ahydroxide, a sulfate, or a phosphate.
 17. The catalyst composition ofclaim 14, wherein each of R¹, R², R³, and R⁴ are an alkyl groupindependently having from 1 to 20 carbons.
 18. The catalyst compositionof claim 14, wherein each of R¹, R², R³, and R⁴ are an alkyl groupindependently having from 4 to 12 carbons.
 19. The catalyst compositionof claim 14, wherein the ammonium salt is tetrabutylammonium chloride ortetradodecylammonium chloride.
 20. The catalyst composition of claim 14,wherein the olefin polymerization catalyst comprises a metallocenecomplex and a cocatalyst comprising a solid super acid (SSA), atrialkylaluminum, an organoaluminoxane, or any combination thereof. 21.The catalyst composition of claim 14, wherein a molar ratio of theammonium salt to the olefin polymerization catalyst is between 0.05 to 1and 0.5 to
 1. 22. A system, comprising: a polymerization reactorcomprising an olefin monomer, a catalyst composition, and a diluent,wherein the polymerization reactor subjects the olefin monomer topolymerization conditions in the presence of the catalyst composition toproduce a polyolefin; and a precontactor coupled to an inlet of thepolymerization reactor wherein the precontactor comprises contactcomponents that form the catalyst composition, the contact componentscomprising: an olefin polymerization catalyst; and an agent comprisingan ammonium salt such that the catalyst composition has a greatercatalyst activity in the presence of water than the olefinpolymerization catalyst where the ammonium salt is not present.
 23. Thesystem of claim 22, wherein the polymerization reactor is a loop slurryreactor.
 24. The system of claim 22, comprising a control system havingone or more tangible, non-transitory, machine-readable mediacollectively storing instructions executable by a processor to: monitorconditions within the polymerization reactor for indicators of anincipient reactor foul; adjust an amount of the agent relative to theolefin polymerization catalyst within the precontactor in response to anindicator of an incipient reactor foul; and controllably introduce thecatalyst composition into the polymerization reactor from theprecontactor.